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The treatment of purified rat muscle AMP deaminase with pryidoxal-5'-P produces a decrease of the enzyme activity which is time- and pyridoxal-5'-P concentration-dependent. The reaction is reversible and can be changed to an irreversible reaction by reduction with NaBH4. The reduced pyridoxal-5'-P-AMP deaminase complex shows an absorption spectrum which is typical for pyridoxamine derivatives. Chromatographic analyses confirm the formation of a Schiff base between pyridoxal-5'-P and the e-amino group of lysine residues in the enzyme. The loss of activity is not a simple inactivation process due to modification of the catalytic site of the enzyme. GTP and ATP, which are allosteric inhibitors of AMP deaminase, show a protective effect against pyridoxal-5'-P inactivation whereas KCl at high concentration exerts a little protection and Pi and P-creatine are ineffective. The reduced pyridoxal-5'-P-AMP deaminase derivative with 30 to 35% residual activity and 6 to 7 moles of pyridoxal-5'-P bound per mole of protein has different kinetic and regulatory properties from the native enzyme: Vmax is the same but the Km value is increased; the enzyme shows a homotropic cooperativity also in the presence of activators, K+ and ADP, and is no longer sensitive to GTP, ATP, and high salt concentration inhibitions. Pi and P-creatine still exert an inhibitory effect. These kinetic properties are similar to those of the native enzyme in the presence of nucleoside triphosphates. The reduced pyridoxal-5'-P-AMP deaminase derivative prepared in the presence of GTP is still sensitive to inhibition by nucleoside triphosphates. It is likely that pyridoxal-5'-P binds at or near the binding sites for these compounds.

1. 1. The effect of K+, nucleoside triphosphates, ADP and Pi on skeletal muscle AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) from frog, pigeon, guinea pig, rabbit and rat, partially purified by the same method, was investigated. 2. 2. K+ activates the enzyme from all the sources; however, the complete activation of rat and pigeon enzymes is observed at KCl concentrations lower than those required for a complete activation of the enzyme from the other sources. 3. 3. At pH 6.5 and at KCl concentrations higher than 100 mM, ATP, GTP, ITP and Pi inhibit the enzyme from all the species examined; however, at 50–100 mM KCl ATP activates the enzyme from guinea pig and rabbit. At pH 7.1 and 50–200 mM KCl ATP inhibits all the enzymes. 4. 4. AMP deaminase is inhibited to a limited extent by nucleoside triphosphates; the inhibition degree depends on the pH and on the sources; Pi completely inhibits the enzyme. Creatine phosphate also is an inhibitor. Kinetic evidences suggest two distinct sites of binding, one for the nucleoside triphosphate and the other for Pi. 5. 5. ADP at low KCl concentrations strongly activates the enzyme, while at high KCl concentrations the activation is weaker or absent; besides this effect ADP removes the inhibition by nucleoside triphosphates and Pi. 6. 6. The data suggest that the enzyme in resting muscle is partially or completely inhibited; when ADP accumulates in muscle it removes the inhibition by nucleoside triphosphates, Pi and creatine phosphate and the enzyme results activated.

The effect of configurational hindrances in unswollen rubberlike networks is taken into account by assuming the existence of a proper correlation between the macroscopic deformation and the rms fluctuations of the network junctions along the various directions of space. Following James and Guth’s approach, some junctions have been fixed at the surface of a proper parallelepiped in order to avoid collapse of the network, and the above correlation is expressed through the introduction of appropriate δ functions into the configurational partition function. Results identical with those previously arrived at by Flory–Hoeve–Ciferri are obtained by assuming that the rms fluctuation components transform as the macroscopic stretch ratios. This assumption cannot hold under high deformations because it implies that the junction fluctuations increase without limit with the deformation. Therefore an intermediate model is proposed where (i) the average ms fluctuations of the junctions are independent of strain, as in J...

The mean‐square distances between various points of regular Gaussian networks are calculated using a new electrical analog and solving exactly a set of difference equations both in two and in three variables through an appropriate Fourier lattice transformation. The results show that the mean‐square radius of gyration of the network is of the same order of magnitude as that of a single chain for networks having a three‐dimensional connectivity, while it increases logarithmically with the total number of chains for networks having a two‐dimensional connectivity.

A new network model is suggested and a constitutive equation is developed on the basis of the assumed validity of Boltzmann's superposition principle for the shear stress. The predictions of the model concerning the relaxation behavior of polymer melts after steady shear or instantaneous deformation are compared to Lodge's theoretical results and to experimental data from the literature.

1. The inactivation of rat skeletal muscle AMP deaminase by Dnp-F (1-fluoro-2,4-dinitrobenzene) is accompanied by the arylation of thiol, amino and phenolic hydroxyl groups. 2. The number of thiol groups that react with Dnp-F is about 12; this is the number that reacts with Nbs2 [5,5′-dithiobis-(2-nitrobenzoic acid)] and N-ethylmaleimide without loss of enzyme activity, and it appears to be the same thiol groups that all three reagents attack. 3. Dinitrophenylation of these reactive SH groups is not the cause of inactivation, since active N-ethylmaleimide-substituted enzyme is also inactivated by Dnp-F.4. Complete inactivation of the N-ethylmaleimide-treated AMP deaminase occurs when about six tyrosine and two lysine residues are dinitrophenylated. 5. Since the treatment of Dnp-enzyme with 2-mercaptoethanol restores much of the enzyme activity, inactivation of AMP deaminase by Dnp-F is probably largely due to modification of tyrosine residues. 6. The kinetic properties of the Dnp-enzyme indicate that a marked decrease in V occurs only after extensive enzyme modification. The decreased activity after slight inactivation results from modification of Km.