Studies of a key protein in the mechanism of the excitation-contraction coupling process of frog skeletal muscle,using phenylglyoxal

The excitation-contraction (E-C) coupling process in single twitch fibres from frog toe muscle was inhibited selectively by phenylglyoxal (PGO), a specific guanidyl modifying reagent. A new protein (31.5 kDa), which has PGO-binding ability and seems to play a key role in the E-C coupling process, was solubilized from transverse tubule membrane-junctional sarcoplasmic reticulum complexes (TTM-JSR) of frog skeletal muscles, using¹⁴C-PGO. The monoclonal antibody against this protein applied extracellularly inhibited the E-C coupling process of the single fibres. This protein appears to constitute the very first step of input for E-C coupling. It is considered to behave as an indispensable part of an electrometer to measure membrane potentials. Therefore, the name electrometrin is suggested for the new protein.     

Pathways of proton transfer in the light-driven pump bacteriorhodopsin

The mechanism of proton transport in the light-driven pump bacteriorhodopsin is beginning to be understood. Light causes the all-trans to 13-cis isomerization of the retinal chromophore. This sets off a sequential and directed series of transient decreases in the pK_a's of a) the retinal Schiff base, b) an extracellular proton release complex which includes asp-85, and c) a cytoplasmic proton uptake complex which includes asp-96. The timing of these pK changes during the photoreaction cycle causes sequential proton transfers which result in the net movement of a proton across the protein, from the cytoplasmic to the extracellular surface.     

Pathways of proton transfer in the light-driven pump bacteriorhodopsin

The mechanism of proton transport in the light-driven pump bacteriorhodopsin is beginning to be understood. Light causes the all-trans to 13-cis isomerization of the retinal chromophore. This sets off a sequential and directed series of transient decreases in the pKa's of a) the retinal Schiff base, b) an extracellular proton release complex which includes asp-85, and c) a cytoplasmic proton uptake complex which includes asp-96. The timing of these pKa changes during the photoreaction cycle causes sequential proton transfers which result in the net movement of a proton across the protein, from the cytoplasmic to the extracellular surface.     

Triphasic vascular effects of thiol compounds and their oxidized forms on dog coronary arteries

The vascular effects of 2-mercaptoethanol, cysteamine, L-cysteine, glutathione (GSH), cystamine and oxidized GSH (GSSG) on the isometric tension of isolated dog coronary arterial strips were examined, and these effects were compared with the triphasic response induced by dithiothreitol (DTT); a rapid and weak contraction (phase A), an intervening slow relaxation (phase B) and a slowly-developing strong contraction (phase C) which we previously reported. The responses of the arteries induced by 2-mercaptoethanol, cysteamine and L-cysteine consisted of phases A, B and C. The order of contractile potency (ED₅₀ of phase C) was DTTL-cysteine>2-mercaptoethanolcysteamine, while the order of relaxant potency (ED₅₀ of phase B) was DTT>cysteamine2-mercaptoethanol. GSSG and cystamine mainly produced relaxation, which corresponded to phase B. The phase C contraction was specific to the reduced forms of thiols, except for GSH, which produced only relaxation. The participation of endothelial cells was not essential for the contracting or relaxing effects of the thiol compounds. The phase C contraction was depressed by W-7, a calmodulin antagonist, while phase A was not. Therefore calmodulin-dependent protein kinases may participate in phase C, not in phase A.     

A 6,000-year sedimentary molecular record of chemocline excursions in the Black Sea

The Black Sea is the world's largest anoxic basin; it is also a contemporary analogue of the environment in which carbonaceous shales and petroleum source beds formed. Recently, Repeta et al. reported that anoxygenic photosynthesis may be an important component of carbon cycling in the present Black Sea, owing to a shoaling of the chemocline and consequent penetration of the photic zone by anaerobic waters in the past few decades. It has been suggested that this was due to an anthropogenic decrease in freshwater input to the Black Sea, although natural causes were not ruled out. Here we report the distributions of sequestered photosynthetic pigments in eight core samples of sediments from the Black Sea ranging in age from zero to 6,200 years before the present. Our results show that photosynthetic green sulphur bacteria (Chlorobiaceae [correction of Clorobiaceae]) have been active in the Black Sea for substantial periods of time in the past. This finding indicates that the penetration of the photic zone by anaerobic waters is not a recent phenomenon, and suggests that natural causes for shoaling of the chemocline are more likely than anthropogenic ones.     

Evaluation of monoaminergic receptors in the genetically epilepsy prone rat

Summary The intensity of sound-induced convulsions in the genetically epilepsy-prone rat (GEPR) was reduced in a dose related fashion by intracerebroventricular administration of dobutamine, (₁ agonist), terbutaline (₂ agonist) or phenylephrine (₁ agonist). BHT-920 (₂ agonist) did not cause a dose-related decrease in sound-induced convulsion intensity. Binding studies showed that whole brain and receptor densities (B_max) were normal while the K_d was increased for the ligand in GEPR brain.Acknowledgment. We are most grateful to Boehringer Ingelheim for generously supplying BHT 920. We are also indebted to Ciba-Geigy Corporation for the gift of terbutaline hydrochloride and phentolamine hydrochloride. The work was supported in part by NIH grant NS 16829.     

Nicotianamine,the ‘normalizing factor’ for the auxotroph tomato mutantChloronerva; a representative of a new class of plant effectors

Summary The article surveys our knowledge of the normalizing factor, gained from its discovery a quarter of a century ago up to the present time, under the following headings: Discovery; Physiological properties; Isolation and characterization; Structure determination (Identity of the normalizing factor with nicotianamine); Chemical properties; Analysis; Synthesis; Occurrence and physiological role; Related compounds; Prospects.     

Physiological state of submitochondrial particles and their susceptibility to Triton X-100

Summary The solubilizing effect of Triton X-100 on beef heart submitochondrial particles (ETP_H) has been studied under various physiological conditions. Coupled, uncoupled and azide-inhibited ETP_H particles have been studied. Quantitative and qualitative differences are found in the proteins solubilized by the detergent from ETP_H particles under the various conditions tested.Acknowledgments: This work was supported in part by a grant from a Spanish Comisión Asesora para la Investigación Cientifica y Técnica. M.C. Barbero was recipient of a scholarship from the Basque Government.     

Isolation and partial characterization of cuticular collagen from the parasitic nematodeGaigeria pachyscelis

Summary The cuticle from adultGaigeria pachyscelis was isolated by solubilizing the internal tissues with sodium dodecyl sulphate (SDS) at 37°C. Cuticular protein was extracted with guanidine-HCl and -mercaptoethanol and purified by ammonium sulphate fractionation and DEAE-cellulose chromatography. SDS-polyacrylamide gel electrophoresis of purified protein revealed 2 polypeptides with apparent mol. wts of 58,000 and 74,000. As judged from their hydroxyproline content both of them are collagenous in nature. Results of gel filtration indicate that cuticular collagen exists in two forms, a non-associated form at low concentration and an associated form at high concentration.Acknowledgments. We thank Drs L.N. Singh and H.C. Tewari for providing the necessary facilities. Laboratory assistance of Mr Ram Kishore is highly appreciated.