Calf diarrhea due to infection by enterotoxigenic Escherichia coli was treated by administration of glycoprotein glycans derived from bovine plasma. The glycan moieties of the nonimmunoglobulin fraction of plasma mimicked the oligosaccharide moiety of intestinal receptors recognized by K99 pili. These glycoprotein glycans inhibited adhesion of E. coli K99+ ST' to erythrocyte glycoconjugates in vitro, and they protected colostrum-deprived newborn calves against lethal doses of enterotoxigenic E. coli (1010 bacteria). Adhesion of bacteria to the intestines (duodenum, jejunum, and ileum) was significantly reduced (by 2 orders of magnitude) in treated calves.

SDS-PAGE and N-terminal sequence analysis of hydrolysis products from 3 substrates containing a unique sensitive bond usually recognized by chymosin (rc-casein, a synthetic hexapeptide and a recombinant tripartite protein) revealed that a 45 kDa endoprotease of Myxococcus xanrhus DKlOl cleaved the same characteristic Phe-Met bond with high specificity. Such an enzyme, easy to obtain from culture supematant and to use in acidic conditions, could be a new tool for protein engineering.

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Leucyl-tRNA and arginyl-tRNA synthetases were purified from wheat embryos by the following purification steps : ammonium sulfate precipitation, gel filtration on Sephadex G-75, chromatographies on DEAE-cellulose and hydroxyapatite, and finally gel electrophoresis.The molecular weights of these enzymes were found to be about 110000 for leucyl-tRNA synthetase and 70 000 for arginyl-tRNA synthetase.Their structures, deduced by dodecylsulfate electrophoresis after reducing treatment, were found to be dimeric for the former and monomeric for the latter. Leucyl-tRNA synthetase exhibits an equilibrium between an active dimeric form and an inactive monomeric form. The number of subunits was determined at dissociation equilibrium by relations deduced from the law of mass action and modified for oligomeric enzymes.When the instantaneous modifications of the activity of these two synthetases are studied in the presence of ribosomes, both activities are slightly stimulated. In addition, when ribosomes (or bovine serum albumin) are preincubated together with the two synthetases, they reduce both the inactivation by dissociation of leucyl-tRNA synthetase and the inactivation (probably by isomerization) of arginyl-tRNA synthetase.Although the ribosomes and bovine serum albumin have apparently similar effects, the great difference in effective concentration between the two, % 1 nM for ribosomes and 30 pM for bovine serum albumin, suggest that the ribosomes have a certain specificity of action; this may involve the maintenance of the synthetases in their conformationally active state.Dimeric aniinoacyl-tRNA synthetases, such as bovine pancreatic tryptophanyl-tRNA synthetase [l], Escherichiu coli prolyl-tRNA synthetase [2] and wheat germ methionyl-tRNA synthetase [3], may dissociate at certain protein concentrations and undergo a partial loss of enzymatic activity. Recent studies, especially with eukaryotic systems, have shown that these enzymes are not free in the intracellular medium, but are associated as multimolecular complexes, occasionally attaining a relatively large size [4-91. They are probably localized on the membranes of the endoplasmic reticulum, in proximity to ribosomes. It is thus probable that synthetases participate in translation processes in the form of integrated sysAbhrrvicrtions. Albumin, bovine serum albumin ; Hepes, 4-(2-hydroxyethy1)-2-piperazineethane sulfonic acid; eEF-1, elongation factor 1 ; eEF-2, elongation factor 2.Definition. A260 unit, quantity of material contained in 1 ml of a solution having an absorbance of 1.0 for 1-cm path length.

SUMMARYAurin tricarboxylic acid (A.T.A.), an inhibitor of protein biosynthesis (initiation and elongation steps), acts also as a competitive inhibitor of phenylalanine, in the ATP-PPi exchange and tRNA Phe aminoacylation reactions catalysed by cytoplasmic wheat germ phenylalanine: tRNA ligase.