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We cloned and sequenced a 2.8-kb SalI fragment of Azospirillum lipoferum FS as a homologue of the Klebsiella oxytoca nifA gene. The amino acid sequence deduced from an open reading frame of 1872 bases showed 91% identity to that of the A. brasilense NifA, and the putative central sigma54 interaction domain was conserved as well as the C-terminal DNA-binding domain. The NifA function on the nifH promoter was examined in Escherichia coli using a combination of a nifA driver plasmid and a nifH-lacZ reporter plasmid, in which the transcriptional activation of the nifH promoter by the NifA was evaluated with the beta-galactosidase activity. The A. lipoferum NifA activated the nifH promoter solely under microaerobic conditions, while the K. oxytoca NifA activated it irrespective of the oxygen condition. These observations suggest that oxygen sensitivity is an intrinsic property of the A. lipoferum NifA.

We studied the difference in the structure of head B (P1-burst head) and head A of myosin by limited tryptic digestion of myosin subfragment-1 (S-1), and using antibodies (anti-A and anti-B) which bind specifically with each head. The antibodies were prepared using peptides with sequences identical to those around the reactive lysine residue of heads A and B. When myosin subfragment-1 (S-1) was cleaved limitedly by trypsin, S-1 heavy chain (100 kDa) was digested into fragments of 25, 50, and 20 kDa. Two fragments with molecular masses of 75 and 27 kDa were transiently produced in the initial phase of digestion. Anti-A and anti-B antibodies bound only with peptides that contained the reactive lysine residue [S-1 heavy chain (100 kDa), 75-, 27-, and 25-kDa peptides], thus showing specific binding with antigen peptide. However, the 27-kDa fragment bound more strongly with anti-B antibody than with anti-A antibody. When S-1 was separated into fractions rich in S-1A and S-1B using insoluble anti-A or anti-B antibody, each antibody bound more strongly with the S-1 heavy chain (100 kDa) of its corresponding fraction by Western immunoblotting. These results suggest that the antibodies react specifically with peptides even after SDS-PAGE and membrane-blotting, and that the structure of the 25 kDa 50 kDa junction differs between heads A and B of myosin.

SUMMARY RDC is a syndrome with unknown etiology that causes rapid destruction of a hip joint. We have investigated the production of osteoclast-activating cytokines (IL-6, IL-1α and tumour necrosis factor-alpha (TNF-α)), interferon-gamma (IFN-γ) and IL-8 by T cells in the affected joint. The level of IL-6 produced by the T cell lines (TCL) established from the femoral head was significantly higher than that from patients' or healthy donors' peripheral blood mononuclear cells (PBMC). IL-6 production by the TCL from synovial membrane or from patients' PBMC was also significantly higher than that from healthy donors' PBMC. IL-1α production by the TCL from the femoral head was significantly higher than any of the other groups when all the TCL were used for the analysis. TNF-α production was highest in the TCL from patients' PBMC. The levels of IFN-γ or IL-8 were not significantly different among these four groups. The plasma levels of all these cytokines except for IFN-γ, that was rather lower, in RDC patients were not significantly different from those in osteoarthrosis or trauma patients, or healthy donors. These results suggest that T cells at the affected femoral head, and also synovial membrane to some extent, are involved in bone resorption through the production of IL-6 and probably IL-1α in patients with RDC.

It was shown by Miyanishi et al. [Miyanishi, T., Maita, T., Matsuda, G., and Tonomura, Y. (1982) J. Biochem. 91, 1845-1853] that the amino acid sequence around the reactive lysine residue is different between head B (Pi-burst head) and head A of the myosin molecule. Thus, we synthesized these two peptides, and prepared rabbit polyclonal antibodies against them. Each antibody bound strongly with both peptides. However, the binding of the antibodies with S-1 was inhibited by the peptide used for the antigen but unaffected by the non-antigen peptide, suggesting that only antibodies specific to each head can bind with S-1. Myosin was absorbed by either antibody A or B, which was immobilized on protein A in Staphylococcus aureus cells. However, half of S-1 was absorbed by each of the antibodies. The S-1 prepared showed about 0.5 mol of initial Pi-liberation per mol of S-1. The Pi-burst size of S-1 unbound to the immobilized anti-A antibody increased to almost 1 mol/mol S-1, while that of S-1 unbound to the anti-B antibody decreased to 0.15 mol/mol S-1. These results suggest the existence of two kinds of heads in the myosin molecule.

Myosins purified from cardiac (porcine heart) and smooth (chicken gizzard) muscles were modified with 2,4,6-trinitrobenzenesulfonate (TNBS) and the effects on the kinetic properties of myosin ATPase [EC 3.6.1.3] were studied. The following results were obtained. 1. About 0.5 mol of TNBS per mol of myosin head was incorporated rapidly, irrespective of the presence of PP1 (2mM), into both types of myosin studied. 2. The size of the initial burst of P1 liberation for both myosins was found to be 0.5--0.6 mol/mol head. 3. The rapid incorporation of TNBS into cardiac muscle myosin was accompanied by a rapid decrease in the size of the initial P1 burst, and it was completely lost after modification for 20 min. However, smooth muscle myosin retained its P1 burst. 4. The EDTA (K+)-ATPase activity of both myosins modified in the presence or absence of PP1 decreased sharply with incorporation of TNBS. 5. Superprecipitation and ATPase activity of reconstituted actomyosin from cardiac myosin and skeletal F-actin decreased only after 10 min of modification with TNBS in the absence of PP1. 6. The spectra of TNP bound to myosins from cardiac and smooth muscles were unchanged by the addition of PP1. The above findings are compared with those previously obtained for skeletal muscle myosin [Miyanishi, T., Inoue, A., & Tonomura, Y. (1979) J. Biochem. 85, 747--753], and the structural and functional differences among the myosins derived from skeletal, cardiac, and smooth muscles are discussed.

The oxygen exchange during ATP hydrolysis by glycerinated muscle fibers, myofibrils, and synthetic actomyosin filaments was studied from the distribution of the [18O]Pi species produced by the hydrolysis of [gamma-18O]ATP. The products were mixtures of two species, one with a low extent of oxygen exchange and the other with a high extent. The low and high extents of oxygen exchange in these two Pi species were the same as those of the acto-S-1 ATPase reaction through the routes with and without the dissociation of actomyosin, respectively (Yasui, M., Ohe, M., Kajita, A., Arata, T., & Inoue, A. [1988] J. Biochem. 104, 550-559). During isometric contraction of glycerinated muscle fibers at 20 degrees C, the fraction of ATP hydrolysis with low extent of oxygen exchange was 0.83 and 0.70, respectively, in 0 and 120 mM KCl. In myofibrils, the fraction of ATP hydrolysis with a low extent of oxygen exchange was 0.72-0.88 in 0-120 mM KCl at 20 degrees C. Therefore, in glycerinated muscle fibers and myofibrils ATP seems to be mainly hydrolyzed through a route without the dissociation of actomyosin, especially at low ionic strength and at room temperature when the tension development is high. ATP hydrolysis through this route may be coupled with muscle contraction.

A myosin-like protein was extracted and partially purified from a flowering plant, Egeria densa. It had no p-nitrophenyl phosphatase activity, but exhibited EDTA(K+)-ATPase [EC 3.6.1.3] activity at high ionic strength. Its molecular weight as estimated by gel filtration was 4-5 X 10(5). The presence of a heavy chain (MW = about 1.8 X 10(5)) was indicated by SDS-gel electrophoresis. Egeria myosin aggregated in an environment of low ionic strength and formed bipolar filaments. It bound with skeletal muscle F-actin with a periodicity of 40 nm.

The rate constants of a series of elementary steps in the H-meromyosin (HMM) Mn2+-ATPase [EC 3.6.1.3] and acto-HMM Mn2+-ATPase reactions were determined in 0.1 M KCl at 5 degrees C. We found that the rate-limiting step in the HMM Mn2+-ATPase reaction was the liberation of ADP from HMM.ADP, of which the rate constant was estimated to be 0.17 s-1. All the results obtained with the acto-HMM Mn2+-ATPase reaction could be quantitatively explained by a modified Lymn-Taylor mechanism (see Fig. 15). The second-order rate constant for the dissociation of acto-HMM induced by ATP was 3.0 X 10(5) M-1.s-1, and that for the Pi burst in the acto-HMM ATPase reaction was 1.7 X 10(5) M-1.s-1. The second-order rate constant for the binding of HMM.ADP with F-actin was 0.25 s-1.mg-1.ml, and the rate-limiting step in the acto-HMM Mn2+-ATPase reaction was the conversion of HMMPADP into HMM.ADP plus Pi, when the F-actin concentration was high.

Two reaction intermediates of H-meromyosin (HMM) ATPase [EC 3.6.1.3], E2AT32P, and (see article), were formed by mixing excess HMM with AT32P. Then a large excess of unlabelled ATP was added, and the amount of AT32P liberated from E2AT32P was measured as the difference between the total amount of AT32P in the reaction mixture and the amount of AT32P bound to HMM, obtained by filtering the mixture after adding charcoal to adsorb nucleotides (charcoal-filtration method). The amount of free AT32P was also measured as the amount of glucose-6-32P formed within 15 sec after adding large excesses of hexokinase [EC 2.7.1.1] and glucose to the reaction mixture. The rate constant, k-2, for the step E2ATP yields E plus ATP was calculated at various KCl concentrations from the time-course of liberation of AT32P. The intermediate, (see article), was formed by mixing HMM with AT32P in a molar ratio of 1:2, and the rate constant, k-6, for the step (see article) was also determined by the same procedures used for k-2. In 0.5 M KCl and 2 mM MgCl2 at pH 7.8 and 0 degrees, k-2 and k-6 were 0.002 sec-1 and 0.1 sec-1 or more, respectively. From the rate constants determined in this work and the rate and equilibrium constants which we reported previously, the standard free energy changes (kcal/mole) for formation of various reaction intermediates in the reaction of HMM ATPase in 0.5 M KCl and 2 mM MgCl2 at pH 7.8 and 0 degrees were calculated to be as follows: (see article).

A fluorescent ATP analog, 2'-(5-dimethylaminonaphthalene-1-sulfonyl)amino-2'-deoxy ATP (DNS-ATP), was synthesized. In water, the wavelengths of maximum excitation were 260 and 340 nm, and that of maximum emission was 554 nm. The fluorescence quantum yield with excitation at 340 nm was 0.052. In 80% dioxane-20% water solution, the wavelength of the maximum emission shifted to 527 nm and the quantum yield was about 5.4 times in water. When DNS-ATP was mixed with HMM in the presence of Mg2+ ions, the fluorescence intensity of DNS-ATP was enhanced by about 30%, and the wavelength of maximum emission shifted to 545 nm. The observed second-order rate constant for the change in fluorescence intensity after adding DNS-ATP to HMM was 1.6 x 10(-7) M-1 . s-1, while the observed first-order rate constant for its recovery was 0.17 s-1. When the HMM DNS-ATPase reaction was measured in terms of the TCA-Pi liberation, 1 mol of initial burst of Pi liberation per mol of myosin was observed. In 50 mM KCl and at 20 degrees C, the rate of the HMM DNS-ATPase reaction was increased by F-actin from 0.4 to 1.15 s-1 (in 3 mg/ml F-actin). The observed dissociation constant for the binding of DNS-ATP with HMM increased from 1.2 to 20 microM in the presence of 5 mg/ml F-actin. However, the extent of change in fluorescence intensity at infinite concentration of DNS-ATP was unaffected by the presence of F-actin.

The species and amounts of intermediates formed by myosin in myofibrils during the ATPase reaction under relaxed conditions were examined. The amount of total nucleotides (ADP + ATP) bound to myofibrils, determined by a centrifugation method or a rapid filtration method, was 0.86 mol/mol myosin head. The amount of bound ADP, determined as the ADP remaining in the mixture after free ADP had been rapidly converted into ATP by an ATP-regenerating system, was found to be 0.67 mol/mol myosin head. We examined the time courses of free-Pi and total-Pi (TCA-Pi) formation after adding ATP to the myofibrils. The amount of Pi bound to myofibrils, calculated by subtracting the burst size of free Pi (0.23 mol/mol myosin head) from that of TCA-Pi (0.60 mol/mol myosin head), was found to be 0.37 mol/mol myosin head. The amount of tightly bound ATP determined by an ATP-quenching method was very low (0.03 mol/mol myosin head). If there is no myosin-phosphate complex, then the amounts of the myosin-phosphate-ADP complex, MADPP, and the tightly bound myosin-ATP complex, M*ATP, are 0.37 and 0.03 mol/mol myosin head, respectively, whereas the amounts of myosin-ADP and loosely bound myosin-ATP complexes are 0.30 and 0.16 mol/mol myosin head, respectively. Thus, half of the myosin heads forms MADPP or M*ATP, and the equilibrium between MADPP and M*ATP shifts to the MADPP side. These results agree with those obtained for myosin in solution (Inoue, A., Takenaka, H., Arata, T., & Tonomura, Y. (1979) Adv. Biophys. 13, 1-194). Therefore, in relaxed myofibrils the active site of myosin does not interact with actin.

2,4-Dinitrophenol (DNP) was found to cause a "clearing response" of myosin B in a medium in which "superprecipitation" of myosin B would otherwise take place. The effect of actin concentration on Mg-ATPase [EC 3.6.1.3] of HMM was studied in the presence and absence of DNP. The results indicate that DNP causes an increase rather than a decrease in the affinity of HMM for actin, and that it causes a decrease only in the actin-activated portion of the Mg-ATPase activity. Using a light-scattering technique, it was shown that neither the ATP-induced dissociation of acto-HMM nor subsequent reassociation is significantly affected by the presence of DNP. As for the formation of the myosin-phosphate-ADP complex in the myosin-ATPase reaction, it was shown that formation of the reactive complex is not affected by DNP. It can thus be concluded that DNP inhibits the decomposition of the actomyosin-phosphate-ADP complex, which is thought to be coupled with superprecipitation.

The oxygen exchange occurring during the acto-S-1 ATPase reaction was analyzed based on the distribution of 18O-labeled species of P1 using [gamma-18O]ATP as a substrate. Evidence was found for the two-route mechanism in which ATP is hydrolyzed via the dissociation of acto-S-1 into F-actin and the S-1-phosphate-ADP complex, S-1PADP, and their recombination, and also hydrolyzed without the dissociation of acto-S-1 (Inoue, A., Shigekawa, M., & Tonomura, Y. (1973) J. Biochem. 74, 923-934; Inoue, A., Ikebe, M., & Tonomura, Y. (1980) J. Biochem. 88, 1663-1677). When ATP was mainly hydrolyzed without the dissociation of acto-S-1, the extent of oxygen exchange was low. When ATP was hydrolyzed by both routes, the distribution of product P1 with 3, 2, 1, and 0 18O atoms showed a mixture resulting from low and high oxygen exchange. The rate of ATPase without the dissociation of acto-S-1 can be estimated from the rate of the overall reaction (v), the rate of recombination of S-1PADP with F-actin (vr), and the extent of dissociation of acto-S-1 (a). The distribution of the P1 species measured was almost equal to that calculated from the ratio of ATP hydrolysis via the two pathways as avr and v-avr, respectively. This result indicates that the rates of the dissociation of acto-S-1PADP into S-1PADP and F-actin and their recombination are much lower than the rate of decomposition of the acto-S-1PADP complex into acto-S-1 + ADP + Pi.

H-Meromyosin (HMM) was digested with insoluble papain [EC 3.4.22.2]. Neither the size of the initial burst of Pi liberation (0.5 mole/mole of myosin head) nor the Mg2+-ATPase [EC 3.6.1.3] activity of HMM in the steady state was affected by this treatment. Acto-S-1 was obtained by mixing F-actin with HMM digested with insoluble papain (HMM-S-1). The size of the initial burst of Pi liberation of acto-S-1 was 0.35 mole/mole of S-l at an ATP concentration of 0.5 mole/mole of S-1, and 0.5 mole/moleof S-1 at ATP concentrations above 1 mole/mole of S-1...

The bindings of S-1 and the two heads of HMM with pyrene-labeled F-actin were studied using the change in light-scattering intensity or that in the fluorescence intensity of the pyrenyl group. At low ionic strength (50 mM KCl), both S-1 and HMM became bound tightly with F-actin (Kd less than 0.1 microM) and both heads of HMM became bound to F-actin. The affinities of S-1 and HMM for F-actin decreased with increasing KCl concentration. In 1 M KCl, the Kd values of S-1 and HMM for F-actin were 11 and 0.58 microM, respectively. Thus, HMM was bound to F-actin 19 times more tightly than S-1. We compared the extent of binding of HMM to F-actin measured by a centrifugation method with that measured by the fluorescence change of pyrenyl-group, and found that even in 1 M KCl, HMM became bound to F-actin with a two-headed attachment. We measured the kinetics of binding and dissociation of acto-S-1 and acto-HMM from the time course of the change in light-scattering intensity after mixing S-1 or HMM with F-actin at 1 M KCl and that after mixing 1 M KCl with acto-S-1 or acto-HMM formed at low ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Myosin was purified rapidly from the nematode Caenorhabditis elegans by an improved method. Crude actomyosin was extracted from the worms at low ionic strength. Paramyosin was removed by repeating the precipitation of myosin filaments in the presence of Mg2+ and the dissolution of them in 0.6 M NaCl. Actin was removed by ultracentrifugation in the presence of Mg-ATP and finally by column chromatography on DEAE-cellulose. This method gave a good yield of myosin (20-30 mg from 50 g wet weight of worms), and its EDTA(K+)-ATPase activity was about 3-fold higher than that of myosin prepared by the method of Harris and Epstein (1979). ATP hydrolysis by nematode myosin showed an initial Pi-burst due to formation of the myosin-phosphate-ADP complex. Tryptophan fluorescence of myosin was enhanced about 8% by ATP. The relationship between the structure and function of myosin is discussed based on the above results and the amino acid sequences of myosins from rabbit skeletal muscle and Caenorhabditis elegans.

The effects of D2O on the elementary steps in the contractile and transport ATPase [EC 3.6.1.3] reactions were studied, and the following results were obtained: 1. The rate of H-meromyosin ATPase in the steady state decreased in D2O to 60% of that in H2O. Deuterium oxide did not affect the size or rate of the initial burst of Pi liberation, i.e. the amount or rate of formation of the reactive myosin-phosphate-ADP complex, MADPP. Moreover, neither the rate of change in the fluorescence spectrum of H-meromyosin induced by ATP (the rate of formation of the second enzyme-ATP complex, M2ATP) nor the rate constant of decomposition of MADPP into M degrees + ADP + Pi was affected by D2O. However, the equilibrium constant of the step M2ATP in equilibrium MADPP decreased in D2O to about 1/2 the value in H2O. 2. In the case of the Na+-K+-dependent ATPase reactin, neither the rate constant of formation of the second enzyme-ATP complex, E2ATP, nor that of decomposition of a phosphorylated intermediate, EADP approximately P, was affected by D2O. However, the equilibrium constant of the step E2ATP in equilibrium EADP approximately P decreased in D2O to about 1/2.5-1/4 of the value in H2O. These results suggest a similarity between the modes of binding of phosphate in MADPP in the myosin ATPase reaction and in EADP approximatley P in the Na+-K+-dependent ATPase reaction.

Previously, several workers reported that at very low ionic strength and in the presence of ATP, the extent of binding of S-1 with the F-actin-tropomyosin-troponin complex or regulated actin (FA-TM-TN) is unaffected by removal of Ca2+. However, in this study we found that during the ATPase reaction at physiological ionic strength, the extent of binding of HMM with FA-TM-TN decreased markedly upon removal of CA2+. Therefore, the effects of Ca2+ were studied on the intermediate steps in the acto-HMM or acto-S-1 ATPase reaction. 1. The nucleotide-induced dissociation of acto-s-1 was studied using AMPPNP as substrate. The extent of binding of S-1 with regulated actin in the presence of Mg2+-AMPPNP increased in a sigmoidal manner as the S-1 concentration increased. When the molar ratio of actin monomer to S-1 was higher than 5-10, the removal of Ca2+ shifted the equilibrium of the dissociation reaction, FA-S-1-AMPPNP in equilibrium FA + S-1-AMPPNP, to the right. 2. The recombination rate of HMMPADP or S-1PADP with regulated actin in the absence of free Mg2+-ATP was estimated by measuring the time course of recovery in light-scattering intensity after addition of ATP. The rate decreased upon removal of Ca2+, when the molar ratio of actin monomer to S-1 was higher than 5-10. 3. The decomposition rate of HMMPADP was measured in the presence of Mg2+-ATP. In the absence of Ca2+, regulated actin did not affect this rate, whereas in its presence, regulated actin markedly accelerated the rate. These findings clearly indicated that at physiological ionic strength, removal of Ca2+ affects various elementary steps in the ATPase reaction to promote the dissociation of myosin heads from FA-TM-TN.

The reaction intermediates formed by the two heads of smooth muscle myosin were studied. The amount of myosin-phosphate-ADP complex, MPADP, formed was measured from the Pi-burst size over a wide range of ATP concentrations. At low concentrations of ATP, the Pi-burst size was 0.5 mol/mol myosin head, and the apparent Kd value was about 0.15 microM. However, at high ATP concentrations, the Pi burst size increased from 0.5 to 0.75 mol/mol myosin head with an observed Kd value of 15 microM. The binding of nucleotides to gizzard myosin during the ATPase reaction was directly measured by a centrifugation method. Myosin bound 0.5 mol of nucleotides (ATP and ADP) with high affinity (Kd congruent to 1 microM) and 0.35 mol of nucleotides with low affinity (Kd = 24 microM) for ATP. These results indicate that gizzard myosin has two kinds of nucleotide binding sites, one of which forms MPADP with high affinity for ATP while the other forms MPADP and MATP with low affinity for ATP. We studied the correlation between the formation of MPADP and the dissociation of actomyosin. The amount of Pi-burst size was not affected by the existence of F-actin, and when 0.5 mol of ATP per mol of myosin head was added to actomyosin (1 mg/ml F-actin, 5 microM myosin at 0 degrees C) most (93%) of the added ATP was hydrolyzed in the Pi-burst phase. All gizzard actomyosin dissociated when 1 mol of ATP per mol myosin head was added to actomyosin.(ABSTRACT TRUNCATED AT 250 WORDS)

F-Actin (FA) and pyruvate kinase (PK) [EC 2.7.1.40] were immobilized on PAB-cellulose. HMM-Subfragment-1 (S-1) was applied to a column of immobilized FA and PK, and eluted with 1-1.5 muM ATP and 1 mM PEP in 50 mM KCl, 2 mM MgCl2, and 10 mM Tris-HCl at pH 7.8 and 4 degrees. The size of the initial burst of Pi liberation of S-1 applied to the column was 0.5 mole/mole S-1. The burst size of S-1 decreased with increase in the fraction number, and S-1 in later fractions showed a burst size of 0.1-0.3 mole/mole. On the other hand, the rate of the ATPase [EC 3.6.1.3] reaction in the steady state was almost independent of the burst size, and increased slightly with increase in the fraction number. The ATPase activity of S-1 with a burst size of less than 0.2 mole/mole was scarcely activated by FA. Usually, the dependence on the burst size of S-1 of its ATPase activity in the presence of FA was sigmoidal, and marked activation by FA was observed when the burst size was larger than 0.3-0.4 mole/mole. Similar results were obtained with S-1 fractions separated by the ultracentrifugation method described in our previous paper ((1976) J. Biochem. 79, 419-434).

The rate constant for the binding of myosin subfragment-1 (S-1) with F-actin in the absence of nucleotide, k1, and that for dissociation of the F-actin-myosin subfragment-1 complex (acto-S-1), k-1, were measured independently. The rate of S-1 binding with F-actin was measured from the time course of the change in the light scattering intensity after mixing S-1 with various concentrations of F-actin and k1 was found to be 2.55 X 10(6) M-1 X S-1 at 20 degrees C. The dissociation rate of acto-S-1 was determined using F-actin labeled with pyrenyl iodoacetamide (Pyr-FA). Pyr-FA, with its fluorescence decreased by binding with S-1, was mixed with acto-S-1 complex and the rate of displacement of F-actin by Pyr-FA was measured from the decrease in the Pyr-FA fluorescence intensity. The k-1 value was calculated to be 8.5 X 10(-3) S-1 (or 0.51 min-1). The value of the dissociation constant of S-1 from acto-S-1 complex, Kd, was calculated from Kd = k-1/k1 to be 3.3 X 10(-9) M at 20 degrees C. Kd was also measured at various temperatures (0-30 degrees C), and the thermodynamic parameters, delta G degree, delta H degree, and delta S degree, were estimated from the temperature dependence of Kd to be -11.3 kcal/mol, +2.5 kcal/mol, and +47 cal/deg . mol, respectively. Thus, the binding of the myosin head with F-actin was shown to be endothermic and entropy-driven.