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Despite extensive studies on [NiFe]-hydrogenases, the mechanism by which these enzymes produce and activate H2so efficiently remains unclear. A well-known EPR-active state produced under H2and known as Ni-C is assigned as a NiIII–FeIIspecies with a hydrido ligand in the bridging position between the two metals. It has long been known that low-temperature photolysis of Ni-C yields distinctive EPR-active states, collectively termed Ni-L, that are attributed to migration of the bridging-H species as a proton; however, Ni-L has mainly been regarded as an artifact with no mechanistic relevance. It is now demonstrated, based on EPR and infrared spectroscopic studies, that the Ni-C to Ni-L interconversion in Hydrogenase-1 (Hyd-1) fromEscherichia coliis a pH-dependent process that proceeds readily in the dark—proton migration from Ni-C being favored as the pH is increased. The persistence of Ni-L in Hyd-1 must relate to unassigned differences in proton affinities of metal and adjacent amino acid sites, although the unusually high reduction potentials of the adjacent Fe–S centers in this O2-tolerant hydrogenase might also be a contributory factor, impeding elementary electron transfer off the [NiFe] site after proton departure. The results provide compelling evidence that Ni-L is a true, albeit elusive, catalytic intermediate of [NiFe]-hydrogenases.

Cancer, development, cellular growth and differentiation are governed by gene expression. Recent molecular and cellular advances to visualize and perturb the pathways of transcriptional regulation, nascent RNA processing, and protein trafficking at the single cell level have been developed. More recently, applications utilizing the green fluorescent marker (GFP) from Aequorea victoria have facilitated visualization of these molecular events in a living cell. Specifically, we will describe a novel approach to perturb cellular processes by labeling discrete cellular components of interest with GFP and subsequently altering/ablating them with a laser microbeam. ©2004 Copyright SPIE - The International Society for Optical Engineering.

Collinear fast-beam laser spectroscopy has been used to measure the hyperfine splittings and the isotope shifts in the 4{ital p}{sup 4}4{ital d} {sup 4}{ital D}{sub 7/2}--4{ital p}{sup 4}5{ital p} {sup 4}{ital P}{degree}{sub 5/2} ({lambda}=729 nm) transition of singly ionized Kr. The measured isotope shifts are very large due to a large specific-mass effect that is caused by the strong momentum correlations of the 4{ital d} electron with the core electrons. Hartree-Fock and multiconfiguration Hartree-Fock (MCHF) calculations of the specific-mass shift were carried out and are compared to the measurements. The MCHF calculation yields excellent agreement with the experimental results.

We compared the abilities of three different calcium (Ca2+) entry blockers, verapamil, diltiazem and felodipine to abolish ouabain-induced ventricular ectopy (100 X ectopic/total beats, VE) in anesthetized, closed-chest dogs. Ventricular tachycardia (VT) was produced in anesthetized, bilaterally vagotomized, closed-chest dogs by an average dose of 65 +/- 19 micrograms/kg ouabain. 30 min after establishing VT, either verapamil (25-50 micrograms/kg + 5-10 micrograms/kg/min), diltiazem (50-100 micrograms/kg + 20-50 micrograms/kg/min), felodipine (3 micrograms/kg + 0.3 micrograms/kg/min) or saline was administered for another 30 min. Verapamil, at the higher dose utilized, practically abolished ouabain-induced VT (97 +/- 3 to 8 +/- 19% VE); diltiazem was moderately effective (96 +/- 4 to 50 +/- 8% ectopy) at 100 micrograms/kg, and felodipine exerted no antiarrhythmic effects in this model. All three Ca2+ entry blockers lowered mean aortic pressure, felodipine lowering this parameter most prominently. Thus, these structurally and electrophysiologically dissimilar Ca2+ entry blockers differed in their abilities to abolish the digitalis glycoside-induced arrhythmias in vivo. The superiority of verapamil may be related to its multiple, additional electrophysiologic effects.

We have previously shown that LHRH agonist [D-Trp6,Pro9-NEt]LHRH (LHRHA) results in reversible oligozoospermia when given to normal subjects for up to ten weeks. A fall in plasma testosterone was accompanied by loss of libido and potency. We now report six subjects who were evaluated by semen analysis and hormone profile at two-week intervals during ten-week basal, 20-week treatment, and post-treatment periods lasting at least ten weeks. Treatment consisted of LHRHA (50 microgram subcutaneously daily), and testosterone enanthate (100 mg intramuscularly every two weeks). Sperm density (mean basal 76.7 +/- 8.7 x 10(6)/ml) fell consistently in each subject to a mean nadir of 12.3 +/- 4.5 x 10(6)/ml (p less than 0.001). This is similar to the mean nadir of 11.6 +/- 5.8 x 10(6)/ml achieved when LHRHA was given alone. In each individual subject, sperm density returned to his basal level after cessation of treatment. No consistent changes were seen in sperm motility of morphology, or in semen volume. Libido and potency were maintained in all subjects. An additional three subjects received testosterone enanthate alone in identical dosage for 20 weeks. No change in sperm density was observed. In contrast to treatment with LHRHA alone, combination treatment produces reversible oligozoospermia without attendant change in potency.

The agonist analogue of gonadotropin-releasing hormone (GnRH), [(imBz1)-D-His6,Pro9-NEt]GnRH, has a potency 200 times that of the native hormone in vitro. In single dose studies in man, this analogue resulted in 2- to 4-fold elevation of LH and FSH, and demonstrated a prolonged duration of activity. [(imBz1)-D-His6,Pro9-NEt]GnRH appears to be safe and, as with other analogues of GnRH, may have application to clinical medicine.