Identification of an essential glutamate residue in the 3-phosphoglycerate kinase of yeast]

The incorporation of nitrotyrosine into 3-phosphoglycerate kinase activated by carbodiimide results in the chemical modification of a single essential residue. After total proteolytic digestion, isolation of the dipeptide gamma Glu-NO2 Tyr by immuno-affinity chromatography indicates the implication of a glutamyl residue. It is interesting to point out the applicability of the method described for the purification of peptides containing carboxyl residues.     

Circadian rhythmicity in phosphorylase activity and glycogen content in the heart muscle of the scorpion,Heterometrus fulvipes,C.L. Koch

Summary Maximal activity levels of phosphorylase A and AB at 20.00 h alternate with minimal levels at 08.00 h of the day, while the glycogen content exhibited a reverse trend in the heart of the scorpion,Heterometrus fulvipes.Acknowledgment. The authors thank Prof. K.S. Swami, for providing facilities. The financial assistance rendered by UGC (to VJ) and ICMR (to DCR) is gratefully acknowledged.     

Zinc binding to peptide analogs of the structural zinc site in alcohol dehydrogenase: Implications for an entatic state

Zinc binding to the peptide replica and analogs to residues 93–115 of horse liver alcohol dehydrogenase (ADH) was examined by competition of the peptides and the chromophoric chelator 4-(2- pyridylazo)resorcinol for zinc and X-ray absorption fine structure analysis of the zinc ligands. In the enzyme, zinc is coordinated by four Cys residues. In the peptide replica, zinc is bound to three Cys and one His residue. A four-Cys zinc coordination is observed only when His is removed, leading to increased zinc stability. ADH crystal structures reveal that the ε-amino group of the conserved residue Lys323 is within H-bond distance of the backbone amide oxygens of residues 103, 105 and 108, likely stabilizing the zinc coordination in the enzyme. The peptide data thus indicate structural strain and increased energy in the zinc-binding site in the protein, characteristic of an entatic state, implying a functional nature for this zinc site. Received 3 July 2008; received after revision 11 August 2008; accepted 1 September 2008     

Tissue distribution and substrate specificity of an epoxide hydrase in the gypsy moth,Lymantria dispar

The stereoselectivity of the enzymatic hydration of disparlure, the pheromone for the gypsy mothLymantria dispar, and for twomeso analogues was determined. A single expoxide hydrase (EH), present in various male and female moth tissues, converted disparlure and the analogues to their respectivethreo-(R,R)-diols with high stereoselectivity as determined by analysis of the diols by chiral phase capillary gas chromatography. This EH recognizes thecis-nature of the dialkyl oxirane, but shows poor discrimination of the two alkyl chains.     

Role of lysosomes, microtubules and microfilaments in the mechanism of the lactogenic action of prolactin in the rabbit mammary gland]

The lysosomotropic agents, ammonium chloride and chloroquine, added to the culture medium of pseudopregnant Rabbit mammary gland, did not inhibit the initiation of casein synthesis by prolactin. By contrast, they considerably reduced the down-regulation of prolacting receptors. Converse-y, colchicine totally blocked the lactogenic action of prolactin without altering the down-regulation of the receptor. Cytochalasin B inhibited only partly the lactogenic action of prolactin while it has no effect on the down-regulation of the receptor. These data suggest that the degradation of the prolactin-receptor complex in lysosome is not a compulsory step in the mechanism of prolactin action. The integrity of microtubules but not of microfilaments is required for prolactin to initiate casein synthesis. These elements of the cytoskeleton are not strictly involved in the down-regulation of the receptor.     

Demonstration of the structural connections of the longitudinal muscle cells and circular muscle cells,and interconnections between the two,in the alimentary canal of an oligochaete,Branchiura sowerbyi B.

Summary The longitudinal and circular muscle cells of the alimentary canal of the oligochaete wormBranchiura sowerbyi show intercell couplings. These couplings occur between adjoining cells of the same or of the other orientation.We wish to thank Dr S. Kawaguti, Prof. emeritus of Okayama University, for his kind advice.     

Enzymatic activities in the liver, and muscle nucleic acids, in swine receiving an unbalanced diet with an excess of methionine for 100 days

Twelve growing Swine were fed an 18% protein diet (Maize and Soja bean) for one hundred days containing either 0,6% sulfur amino acids (basal diet) or 0,6% and 1% DL-methionine added to the control diet. Such an excess, reduced food intake and body weight gain mainly during the "finishing period" (60 to 100 kg). The RNA/DNA and protein/DNA ratios in the muscle did not show any difference. Hepatic activities of some enzymes involved in glycolysis, gluconeogenesis and amino acid metabolism, were unchanged, except that of methionine adenosyl transferase, the first step of transsulfuration, which was induced in proportion with the amount of the methionine ingested. Swine seemed to adapt to the excessive methionine intake, which did not show any toxicity in our experimental conditions.     

Action of an ATP analog, adenosine 5'-hyophosphophosphate in the reactions catalysed by hexokinase and fructose-6-phosphate kinase]

Adenosine 5'-hypoposphate phosphorylates glucose and fructose 6-phosphate in the presence of hexokinase and fructose 6-phosphate kinase respectively. It behaves as a competitive inhibitor versus ATP in the hexokinase reaction. Its affinity for the two enzymes is similar to that of ATP, the maximal velocities being however much lower.     

Chemical analysis of the integument and digestive gland of Crangon crangon (Linné) (Crustacea, Decapoda) by x ray spectography. Quantitative variations in the elements of calcium, phosphorus, sulfur, and magnesium during the intermolt cycle]

Electron probe microanalysis is a very suitable method for qualitative and quantitative analysis of calcium, phosphorus, sulfur and magnesium occurring within integument and digestive gland; variations related to intermolt cycle can be compared.     

Rp-diastereomer of adenosine cyclic 3',5'-phosphorothioate as an antagonist of the stimulatory action of cyclic AMP on the ouabain-insensitive Na efflux in single barnacle muscle fibers

Single muscle fibers of the barnacle Balanus nubilus have been used as a preparation to test the possibility that the Rp-diastereomer of adenosine cyclic 3',5'-phosphorothioate, which is the first available analog of cAMP that acts as an antagonist of cAMP, may reduce the magnitude of cAMP-mediated stimulation of the resting ouabain-insensitive Na efflux. The results obtained show that this antagonist is, in fact, able to reduce stimulation of the Na efflux by injected cAMP in a dose-dependent manner.     

Comparison of glutamate dehydrogenase and glutamine synthetase activities in the roots and aerial organs of an obligate halophyte: Suaeda maritima var. macrocarpa and a glycophyte: Phaseolus vulgaris, grown in presence of different concentration of NaCl]

The glutamate dehydrogenase and glutamine synthetase activities of an obligate halophyte, Suaeda maritima var. macrocarpa and a glycophyte. Phaseolus vulgaris are compared in function of salinity (increasing concentrations of NaCl) of the culturing solution. In culture, addition of NaCl stimulates glutamine synthetase activity and lowers glutamine dehydrogenase activity in the aerial organs and in the roots of Suaeda as opposed to what is observed in the glycophyte. Hence the obligatory halophily of Suaeda is related to an increase of the glutamine synthetase activity in a sal-trich medium corresponding to the stimulation of nitrate reductase and proteogenesis.