The stereochemistry of the L-histidinol dehydrogenase reaction was determined to be R at NAD for both steps, confirming previous results with a fungal extract [Davies, D., Teixeira, A., & Kenworthy, P. (1972) Biochem. J. 127, 335-343]. NMR analysis of monodeuteriohistidinols produced by histidinol/NADH exchange reactions arising via reversal of the alcohol oxidation reaction indicated a single stereochemistry at histidinol for that step. Comparison of vicinal coupling values of the exchange products with those of L-alaninol and a series of (S)-2-amino-1-alcohols allowed identification of the absolute stereochemistry of monodeuteriohistidinols and showed that histidinol dehydrogenase removes first the pro-S then the pro-R hydrogens of substrate histidinol. The enzyme stereochemistry was confirmed by isotope effects for monodeuteriohistidinols as substrates for the pro-R-specific dehydrogenation catalyzed by liver alcohol dehydrogenase. Active site mapping was undertaken to investigate substrate-protein interactions elsewhere in the histidinol binding site. Critical binding regions are the side-chain amino group and the imidazole ring, whose methylation at the 1- or 2-position caused severe decreases in binding affinity. Use of alternative substrates further clarified active site interactions with the substrate. Compounds in which the alpha-amino group was replaced by chloro, bromo, or hydrogen substituents were not substrates of the overall reaction at 1/10,000 the normal rate.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

We present a novel technique of nerve repair attempting to reduce scarring and improve alignment. A laser solder composed of albumin, hyaluronate and indocyanine green dye (peak absorbance 805 nm) was used. After applying solder to the anastomotic site, nerve ends can be precisely aligned and sealed in place using an 81 0 nm diode laser. Transected sciatic nerves in the rat were used as the experimental model. Laser repairs had approximately half the immediate strength of suture repairs (130 vs. 280 g/cm) but comparable strength by 7 days (270 vs. 250 g/cm2). There was no dehiscence in either group. Thermal damage was confined to the solder and epineurium. At 90 days there was no difference in nerve conduction values or axon counts in suture or laser repairs. Histology was suggestive of a later stage of regeneration in the laser group. Laser soldering produces increased strength compared with traditional laser welding with less thermal injury. Laser soldering could provide a viable alternative to sutured nerve repair with the advantages of greater ease and speed as well as less tissue injury and an improved functional result.

It is well known that under different physiological and pathologic conditions, the atrioventricular junction (AVJ) may become the pacemaker of the heart. However, unlike the well-characterized AVJ pacemaker in animal models, autonomic control of the human AVJ pacemaker has not been studied. Explanted human hearts with different types of cardiomyopathy (n=7) were obtained at the time of cardiac transplantation and perfused with cardioplegic solution. The AVJ was cannulated, isolated from the rest of the heart, immobilized with the excitation-contraction uncoupler blebbistatin (10 μmol/L) and optically mapped using the infrared voltage sensitive dye di-ANBDQBS. Imaging was conducted with 100x100 CMOS camera from endocardial field of view ranging 24x24 to 36x36mm 2 , which allowed to simultaneously map right side of intratrial and intraventricular septa, coronary sinus (CS) and His bundle regions. In control, we found AVJ rhythm of 31+/−15 bpm (2409+/−1264 ms) in all human preparations which originated in compact AV node (N-region, n=4) and/or region between AV node and His bundle (NH-region, n=3). Isoproternol (Iso, 1 μM) induced AVJ rhythm acceleration up to 68+/−12 bpm (913+/−192 ms), temporary pacemaker shift to CS region (n=2) and improved conduction in both slow and fast pathways, which induced reentrant arrhythmias in 3/5 preparations. Acetylcholine (ACh, 1–3 μM) slowed rhythm to 21+/−6 bpm (3130+/−1146 ms) and conduction in both pathways up to complete block, and induced temporary pacemaker shift to CS region in 3/4 preparations. Moreover, we found bifocal activation in 3/4 preparation when two main pacemakers (CS and compact AV node) worked asynchronously with different frequencies, accompanied by the exit block from AV node. We showed by high-resolution optical mapping for the first time that unlike in animal models (rabbit and rat) in isolated coronary perfused human AVJ leading pacemaker localized mostly in the N- or NH-regions. Beta-adrenergic (Iso) and cholinergic (ACh) stimulations of AVJ can significantly accelerate or slow rhythm and conduction, as well as induced pacemaker shift to CS, and result in reentrant arrhythmias. This research has received full or partial funding support from the American Heart Association, AHA Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).