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.     

Biology of halophilic bacteria,Part II

Archaebacteria (archaea) are comprised of three groups of prokaryotes: extreme halophiles, methanogens and thermoacidophiles (extreme thermophiles). Their membrane phospholipids and glycolipids are derived entirely from a saturated, isopranoid glycerol diether,sn-2,3-diphytanylglycerol (archaeol) and/or its dimer, dibiphytanyldiglyceroltetraether (caldarchaeol). In extreme halophiles, the major phospholipid is the archaeol analogue of phosphatidylglycerolmethylphosphate (PGP-Me); the glycolipids are sulfated and/or unsulfated glycosyl archaeols with diverse carbohydrate structure characteristic of taxons on the generic level. Biosynthesis of these archaeol-derived polar lipids occurs in a multienzyme, membrane-bound system that is absolutely dependent on high salt concentration (4 M). The highly complex biosynthetic pathways involve intermediates containing glycerol ether-linked C₂₀-isoprenyl groups which are reduced to phytanyl groups to give the final saturated polar lipids. In methanogens, polar lipids are derived both from archaeol and caldarchaeol, and thermoacidophiles contain essentially only caldarchaeol-derived polar lipids. The function of these membrane polar lipids in maintaining the stability, fluidity and ionic properties of the cell membrane of extreme halophiles, as well as the evolutionary implications of the archaeol and caldarchaeol-derived structures will be discussed.     

Hepatic glucose signals vagally modulate the cyclicity of gastric motility in rats

The cyclicity and intensity of gastric motlity were examined following glucose injection into the portal vein with an intragastric balloon in anesthetized rats. Enhanced gastric motility caused by insulin administration was influenced by 4 mM glucose (25 l) injected into the portal vein; glucose provoked a shift in the cyclicity power spectrum without any change in intensity. The peak power spectrum shifted from 4.0–5.0 cpm to 2.0–3.0 cpm. Hepatic branch vagotomy abolished the response.The results suggest that glucose signals in the hepatic vagal branch modulate the cyclicity of gastric motiligy.     

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.     

Some citrus chitinases also possess chitosanase activities

Several acidic chitinase and chitosanase isoforms were found in 4-week-old nonembryogenic sweet orange (Valencia [Citrus sinensis (L.) Osbeck]) callus tissue. Two isoforms (designated A1-CF1 and A1-CF2) were purified to homogeneity using HPLC size exclusion, anion exchange, and chromatofocusing techniques. Both hydrolase isoforms exhibited activity with either colloidal chitin or solubilized shrimp shell chitosan. Specific activities for the purified isoforms could not be calculated because of the lack of protein and contamination of ampholytes. However, the specific activities for chitinase and chitosanase after anion exchange were respectively 404 nmol GlcNAc per min per mg protein and 2,475 nmol GlcN per min per mg protein. The M_r for both enzymes was 30,500. The homogeneous proteins cross-reacted in western blots with antiserum against a basic class I potato leaf chitinase.     

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.     

Mitochondrial DNA evidence for the 19th century introduction of African honey bees into the United States

Since the introduction of an African subspecies into Brazil in the mid-1950's¹, descendent Africanized honey bees (Apis mellifera L.) have spread throughout the Neotropics and into temperate North America. Restriction enzyme analysis of 422 feral honey bee colonies collected from non-Africanized areas in the southern United States revealed that over 21% of them had mitochondrial DNA (mtDNA) derived from a European race established in North America by the 17th century, 77% of them had mtDNA common in honey bees maintained by beekeepers and about 1% exhibited African mtDNA. Further analysis revealed that the African mtDNA was derived from a north African subspecies imported to the US in the 19th century.     

Differential sensitivity to ethidium bromide of replicative DNA synthesis and bleomycin-induced unscheduled DNA synthesis in permeable mouse sarcoma cells1

Summary Replicative DNA synthesis in permeable mouse sarcoma cells was more sensitive to ethidium bromide (EtBr) than bleomycin-induced unscheduled DNA synthesis (UDS). A similar difference in sensitivity to EtBr was observed between DNA polymerases and . The difference in sensitivity to EtBr of replicative DNA synthesis and UDS in the present system seems to reflect mainly the sensitivity difference between DNA polymerases and .Acknowledgments. The authors wish to thank Nippon Kayaku Co. (Tokyo, Japan) for providing copper-free bleomycin A₂. This research was supported in part by a grant from the Japan Ministry of Education, Science and Culture.     

Cyclophosphamide-impaired regulation of hepatic heme metabolism

Summary Im male rats hepatic cytochromes b₅ and P-450 were reduced at different times after treatment with cyclophosphamide (CP) (200 mg/kg i.p. for 3 days). In contrast, microsomal heme did not change until 48 h after the last dose of CP, leading to accumulation of heme in a non-cytochromal form. Parallel to the above changes the heme metabolism showed derangement: -aminolaevulinate synthase, the rate-limiting enzyme in heme synthesis, was depressed and heme oxygenase, the enzyme which catalyzes the oxidative degradation of heme, was increased.