Bacterial leader peptidase,a membrane protein without a leader peptide,uses the same export pathway as pre-secretory proteins

Leader peptidase typifies a group of proteins of the plasma membrane of E. coli which span the membrane and are synthesized without a cleaved amino-terminal leader (signal) sequence. The membrane assembly properties of these proteins have not been previously reported. We find that the membrane electrochemical potential is necessary for the insertion of a large domain of leader peptidase across the membrane. In the absence of potential, the peptidase accumulates inside the cell in tight association with the. plasma membrane. Upon restoration of the potential, accumulated peptidase inserts across the membrane, indicating that this insertion is not mechanistically coupled to polypeptide chain growth. The normal, trans-bilayer peptidase and that which accumulates in the absence of potential have different conformations, as shown by the relative resistance of the trans-bilayer enzyme to digestion by trypsin or chymotrypsin in cell lysates. Membrane insertion is accompanied by this conformational change. This assembly reaction has several features predicted by the hypothesis of membrane-triggered folding.     

Production of penicillins and cephalosporins in an immobilized enzyme reactor

Summary Four enzymes required for the biosynthesis of pencillins and cephalosporins by Streptomyces clavuligerus have been immobilized on an anion exchange resin. The capabilities of the system have been studied by circulation of reaction mixtures through the immobilized enzyme reactor. Within 30 min, all of the substrate -(l--aminoadipyl)-l-cysteinyl-d-valine is consumed and converted to a mixture of penicillins and cephalosporins. After 60 min the major antibiotic products are (iso)penicillin N and desacetylcephalosporin C. The activity of the immobilized enzyme reactor activity is stable to storage at temperatures below 4°C but activity is lost on repeated use.     

Protamines in plant sperm

Sperm protamines have been isolated from representatives of three major plant groups: algae (Chara corallina ), bryophytes ( Marchantia polymorpha), and ferns ( Marsilea vestitia ). We previously reported the complete displacement of histones by protamines in Marchantia (Reynolds W F & Wolfe, S L, Exp cell res 116 (1978) 269 [8] ). Marchantia protamines appear as four components on acid-urea gels, whereas Chara and Marsilea protamines comigrate as a single band with a mobility comparable to salmon protamine. The amino acid compositions of the plant protamines show these to be arginine-rich, highly basic (35-42%) proteins which display overall similarity in amino acid composition (84-91%). The molecular weights of Chara and Marsilea protamines are approx. 4700-5300 D.     

Increase of unesterified fatty acids, prostaglandin F2α but not thromboxane B2 in rat brain during drug induced convulsions

The amount of free arachidonic acid and prostaglandin F_2α in rat cerebral hemispheres was increased following convulsions induced by carbachol and metrazol. The level of thromboxane B₂ was not affected and prostaglandin endoperoxides could only be “trapped” after a very short convulsive period. Unesterified fatty acid levels at 2 minutes post-mortem were decreased by 50% in the cerebral hemispheres of phenytoin treated rats. Under the same conditions, phenobarbital and diazepam had little effect on the levels of free fatty acids in rat brain.     

Determination of the solution conformation of adenosein 2':3'-monophosphate by nuclear magnetic resonance with lanthanide probes.

The aqueous solution conformation of adenosine 2':3'-monophosphate at pH 2.5 has been determined by a nuclear magnetic resonance method utilizing lanthanide ions as shift and relaxation probes. The ribose conformation is best described as a rapid equilibrium of 2'-endo(3'-exo) and 3'-endo(2'-exo) conformations in a ratio of approximately 2 to 1. The orientation of the base relative to ribose is restricted to a narrow range about chiCN=-70 degrees.     

Effects on Sperm Morphology by Alleles at the Pink-Eyed Dilution Locus in Mice

Sperm head morphology was analyzed in all genotypic combinations for alleles dark pink-eye (p^d) and p-sterile alleles, p^6H, p^bs (p -black-eyed sterile) and p^25H. Three of these, p^6H, p^bs and p^25H, were radiation induced; homozygotes and heterozygotes of these three alleles are male sterile, whereas p^d/— genotypes are fertile. Sperm heads were examined by light microscopy and assigned to one of five classes: A. normal and near-normal, B. triangulate and oblate, C. spatulate, D. elongate, and E. filamentous. Males of each sterile genotype had grossly abnormal sperm and each sterile genotype differed from all other sterile genotypes and from fertile genotypes in at least one class, except p^6H/p^6H compared to p^bs/p^bs.Frequency distribution profiles (1) revealed a complex pattern of allelic interaction and do not support a deletion-complementation hypothesis, (2) do not show simple bimodality, which might suggest post-meiotic (haploid) gene expression, and (3) together with unpublished breeding data, show that p^25H is not a remutation of p^6H.     

Modification of ribonucleic acid by vitamin B6. 1. Specific interaction of pyridoxal 5'-phosphate with transfer ribonucleic acid.

Whole tRNA preparation obtained from a human cell line (HT-29) of colon carcinoma and purified specific Escherichia coli tRNA were reacted with pyridoxal 5'-phosphate, reduced by sodium borohydride and digested with RNase A and snake venom phosphodiesterase. Two-dimensional chromatography of the pyridoxal 5'-phosphate treated tRNA digest showed that pyridoxal 5'-phosphate binds specifically to GMP, presumably in the form of a Schiff base with the exocyclic amino group of the purine. The reaction of pyridoxal 5'-phosphate with whole tRNA was competitively inhibited by N-acetoxy-2-acetylaminofluorene. This suggests that binding occurred primarily to the G20 base residue at the unpaired region of the dihydrouridine loop (Fujimura et al., 1972). The modification of tRNA by pyridoxal 5'-phosphate resulted in the inhibition, to varying extent (10-80%), of amino acid acceptance in the aminoacyl-tRNA synthetase reaction. Defects in codon recognition by pyridoxal 5'-phosphate modified amino acid acylated tRNAs in the presence of the corresponding guanine-containing polynucleotide triplets were observed by the ribosomal binding assay.     

Nutrition and carbon metabolism of Methanococcus voltae.

Methanococcus voltae is a heterotrophic, H2-oxidizing methanogenic bacterium. In complex medium, this bacterium has a doubling time of 1.2 h at its temperature optimum of 38 degrees C. In defined medium, optimal growth is obtained with 0.75 mM isoleucine, 0.75 mM leucine, 2.5 mM acetate, 5 mM NH4Cl, 84 mM MgSO4, 0.4 M NaCl, 1 mM CaCl2, 10 microM Fe2O3, and 0.2 microM NiCl2. In addition, pantothenate, sodium selenate, and cobalt stimulate growth. Optimal growth is obtained between pH 6.0 and 7.0 with either H2 or formate as the electron donor. The volatile fatty acids 2-methylbutyrate and isovalerate can substitute for isoleucine and leucine, respectively. Cellular carbon is derived from acetate (31%), isoleucine (22%), leucine (25%), and carbon dioxide (23%). The amino acids and fatty acids are incorporated almost exclusively into protein. A comparison of the incorporation of U-14C-amino acids and 1-14C-fatty acids indicated that the fatty acids are degraded during incorporation into cell protein. The distribution of carbon from the amino acids suggests that acetyl coenzyme A is not a major intermediate in the degradation of these compounds. Thus, M. voltae may convert isoleucine and leucine to other amino acids by a unique mechanism. The lipid carbon is derived largely from acetate. Thus, the isoprenoid lipids are synthesized de novo from acetate rather than by degradation of leucine. The carbon in the nucleic acids is derived from carbon dioxide (45%), the C-1 of acetate (25%), the C-2 of acetate (22%), and isoleucine and leucine (7%). This labeling pattern is consistent with known biochemical pathways.