Modification by simetryn sulphoxide of a specific thiol group in rat haemoglobin.

Native rat haemoglobins were found to bind simetryn sulphoxide to an extent 40-fold greater than human haemoglobin. This specific behaviour was studied by using only high-pressure ('performance') liquid chromatography for the preparative separation of globin chains and the isolation of peptides resulting from chemical and enzymic degradation. High recoveries (greater than 80%) of peptides throughout the procedures in combination with microsequence techniques, allow a definitive assignment of the residue undergoing modification. The haemoglobin beta-chain cystine-125 residue, with a stoichiometry of one per tetramer of rat haemoglobin, was found to be modified. Stereochemical implications of this finding are discussed. Simetryn sulphoxide would appear to be useful as a specific reagent for the mapping of exposed thiol residues in proteins.     

Influence of dicarboxylic phosphatidylcholines on phosphatidylcholine liposomes as revealed by gel chromatography and electron microscopy

The effect of dicarboxylic phosphatidylcholines (glutarylphosphatidylcholine) on the structural changes of phosphatidylcholine liposomes is examined by using multilamellar liposomes prepared with egg phosphatidylcholine or dipalmitoylphosphatidylcholine and by varying the surface charge by addition of dicetyl phosphate. Investigations are performed by gel chromatography and electron microscopy. Glutarylphosphatidylcholine is in micellar form (rod-like micelles or globular micelles). The structures obtained depend on the fatty acid saturation of liposomes and on the charge of liposome (addition or not of dicetyl phosphate). With egg phosphatidylcholine/glutarylphosphatidylcholine dispersions, an aspect more similar to myelinic figures than liposomes is observed, while in the presence of dicetyl phosphate, liposomes similar to control egg phosphatidylcholine liposomes are obtained. Gel chromatography on Sepharose 4B and turbidity measurements prove that dicetyl phosphate increases the stability of egg phosphatidylcholine/glutarylphosphatidylcholine mixtures. On the other hand, in dipalmitoylphosphatidylcholine/glutarylphosphatidylcholine dispersions, incorporation of dicetyl phosphate destabilizes bilayer structure and the formation of mixed micelles occurs. Viscosity measurement shows, in the presence of dicetyl phosphate, an increased fluidity for dipalmitoylphosphatidylcholine/glutarylphosphatidylcholine dispersions, in agreement with the micellar organization. These data confirm that the disorganization of liposomal membranes by dicarboxylic phosphatidylcholine depends on the fatty acid composition of phosphatidylcholine and on the presence of dicetyl phosphate.     

Mitochondrial DNA evolution in lagomorphs: Origin of systematic heteroplasmy and organization of diversity in European rabbits

Summary A characterization was conducted on mitochondrial DNA (mtDNA) molecules extracted separately from 107 European rabbits (Oryctolagus cuniculus) both wild and domestic, 13 European hares (Lepus capensis), and 1 eastern cottontail (Sylvilagus floridanus). Experimentally this study took into account restriction site polymorphism, overall length variation of the noncoding region, and numbers of repeated sequences. Nucleotide divergences indicate that the mtDNAs from the three species derived from a common ancestor some 6–8 million years (Myr) ago. Every animal appeared heteroplasmic for a set of molecules with various lengths of the noncoding region and variable numbers of repeated sequences that contribute to them. This systematic heteroplasmy, most probably generated by a rate of localized mtDNA rearrangements high enough to counterbalance the cellular segregation of rearranged molecules, is a shared derived character of leporids.The geographic distribution of mtDNA polymorphism among wild rabbit populations over the western European basin shows that two molecular lineages are represented, one in southern Spain, the second over northern Spain, France, and Tunisia. These two lineages derived from a common ancestor some 2 Myr ago. Their present geographical distribution may be correlated to the separation of rabbits into two stocks at the time of Mindel glaciation.Finally the distribution of mtDNA diversity exhibits a mosaic pattern both at inter- and intrapopulation levels.     

Ferredoxin-dependent methane formation from acetate in cell extracts of Methanosarcina barkeri (strain MS).

Cell extracts of Methanosarcina barkeri grown on acetate catalyzed the conversion of acetyl-CoA to CO2 and CH4 at a specific rate of 50 nmol min-1 mg-1. When ferredoxin was removed from the extracts by DEAE-Sephacel anion exchange chromatography, the extracts were inactive but full activity was restored upon addition of purified ferredoxin from M. barkeri or from Clostridium pasteurianum. The apparent Km for ferredoxin from M. barkeri was determined to be 2.5 M. A ferredoxin dependence was also found for the formation of CO2, H2 and methylcoenzyme M from acetyl-CoA, when methane formation was inhibited by bromoethanesulfonate. Reduction of methyl-coenzyme M with H2 did not require ferredoxin. These and other data indicate that ferredoxin is involved as electron carrier in methanogenesis from acetate. Methanogenesis from acetyl-CoA in cell extracts was not dependent on the membrane fraction, which contains the cytochromes.     

Effects of invertebrate predation on the seasonal succession of a zooplankton community: a two year study in Lake Aydat,France

Saline playa lakes represent major geomorphic and hydrologic components of internal drainage basins in the arid to semiarid interior of Australia. These lakes mark the outcrop areas of regional shallow groundwater; thus, they are effective hydro-chemical sinks for elemental concentration and authigenic formation of carbonate, evaporite, and silica/silicate minerals.Field observations and petrochemical characterization of playa sediments from drainage basins in Western and Central Australia indicate that localized discharge of groundwater, from shallow aquifers in calcrete deposits, plays a fundamental role in geochemical evolution of playa-lake marginal facies. The available data indicates also that although evaporative concentration and salt recycling are major controls on geochemistry of the playas, yet a simple evaporative concentration model does not provide a complete explanation for brine evolution and particularly the geochemical process-product relationships observed in the individual playa lakes. The distribution of the chemical facies in the playas, in relation to geomorphic setting of the internal drainage basins, reflects a significant impact of variation in groundwater discharge pattern on the geochemical evolution of the playa lakes. Accordingly, the development of chemical facies in individual playas have progressed through repeated episodes of evaporative concentration, groundwater-level fluctuations and ion-exchange processes.     

Purification and characterization of catalytic fragments of phosphorylase kinase gamma subunit missing a calmodulin-binding domain

A catalytic fragment preparation of rabbit muscle phosphorylase kinase produced by limited chymotryptic digestion was isolated and identified as the NH2-terminal region of the gamma subunit by Edman degradation. Mass spectral analysis, gas phase sequence analysis, and amino acid analysis of the active fragment carboxyl-terminal peptides revealed multiple COOH termini generated at residues Tyr290, Arg296, and Phe298 in the gamma subunit sequence. These active fragment species are about 24% smaller than the gamma subunit (Mr 44,673) and range in size from Mr 33,279 to Mr 34,275. The active fragment preparation exhibits a specific activity about 6-fold higher than that of the gamma subunit-calmodulin complex. Calmodulin confers calcium sensitivity to the gamma subunit but has no effect on the enzymatic properties of active fragment. Affinity measurements demonstrated a dissociation constant of 0.7 microM for active fragment binding to dansylcalmodulin, a value about 28-fold weaker than reported for the gamma subunit. These data support the presence of a calmodulin binding domain in the COOH-terminal region of the gamma subunit.