Nitrite reduction in Bacteroids of Rhizobium “hedysari” strain HCNT 1

Ex planta, bacteroids of the sulla-symbiont Rhizobium hedysari strain HCNT 1 terminated reduction of nitrite at nitrous oxide irrespective of the presence or absence of acetylene. Nitrate was not reduced during the experimental period, but slight nitrate reductase activity occurred if incubation with nitrate was prolonged (up to 15 h). As was observed in free-living cells, exposure of the bacteroids to the metal chelator, diethyldithiocarbamate, prevented reduction of nitrite, indicating the presence of a copper-containing nitrite reductase. Pulses of 10–75 M nitrite transiently impeded O₂ uptake in bacteroids, which resumed consumption of O₂ when the nitrite had been reduced. Exposure to >1.0 mM nitrite for 24h greatly inhibited nitrogenase activity (assayed as acetylene reduction activity) of bacteroids in planta. Exposure to the same concentrations of nitrite after 1h of incubation in the presence of acetylene almost completely stopped ongoing ethylene production in bacteroids of strain HCNT 1 extracted from nodules. Free cells of the non-nitrite-reducing R. hedysari strain CC 1335 were lacking in nitrogenase (acetylene-reduction) activity, whereas identically cultured (low-oxygen) strain HCNT 1 cells reduced both nitrite and acetylene.Abbreviations PMS phenazine methosulfate - DDC diethyldithiocarbamate     

Catabolism of dl-α-phenylhydracrylic,phenylacetic and 3- and 4-hydroxyphenylacetic acid via homogentisic acid in a Flavobacterium sp.

A degradation pathway for dl--phenylhydracrylic, phenylacetic, 3- and 4-hydroxyphenylacetic acid by a Flavobacterium is presented. Experiments with washed cells and enzyme studies revealed that dl--phenylhydracrylic acid in an initial reaction was oxidatively decarboxylated to phenylacetaldehyde. Whole cells oxidized both stereoisomers of phenylhydracrylic acid at different rates. The product phenylacetaldehyde in turn was oxidized to phenylacetic acid. No hydroxylation of phenylacetic acid was detected in cell extracts, but on the basis of experiments with washed cells it is assumed that phenylacetic acid is mainly metabolized via 3-hydroxyphenylacetic acid. This latter product was subsequently hydroxylated yielding the ring-cleavage substrate homogentisate. 4-Hydroxyphenylacetic acid was also degraded via homogentisate. Ringcleavage of homogentisate gave maleylacetoacetate which was further degraded through a glutathione-dependent pathway. Homoprotocatechuate was not an intermediate in the metabolism of dl-phenylhydracrylic acid, phenylacetic, 3- and 4-hydroxyphenylacetic acid metabolism, but it could be hydroxylated aspecifically to 2,4,5-trihydroxyphenylacetic acid by the action of the 3-hydroxyphenylacetic acid-6-hydroxylase.Abbreviations HPLC high-performance liquid chromatography - PHA phenylhydracrylic acid - PA phenylacetic acid - HPA hyxdroxyphenylacetic acid - PMS phenazine methosulphate - PMA phenylmalonic acid - GSH glutathione     

Structural studies on cyanobacterial photosystem I

The cyanobacterial photosystem, I complex from Synechococcus sp. PCC6301 contains polypeptides of apparent M_r of 70,000, 18,000, 17,700, 16,000 and 10,000. Procedures were developed for the purification of the M_r 17,700 and 10,000 polypeptides. Amino acid analyses showed the absence of cystine and cysteine from these polypeptides. Amino-terminal sequences of 98 residues for the M_r 17,700 polypeptide and of 42 residues for the M_r 10,000 polypeptide were determined. Studies of pigment distribution within the photosystem I complex indicated that the binding of chlorophyll a and -carotene is in part dependent on the presence of these polypeptides.Abbreviations PSI photosystem I - P700 reaction center of PSI - SDS sodium dodecylsulfate - TBS tris-buffered saline - TTBS TBS containing Tween-20     

Purification and characterisation of an inducible β-galactosidase from Corynebacterium murisepticum

The -galactosidase (EC 3.2.1.32) of Corynebacterium murisepticum (inducible by lactose and galactose) was purified by successive column chromatography on Sephadex G-200, DEAE-Sephadex A-50 and DEAE-cellulose (DE52). The enzyme was found to be a dimer of identical subunits of molecular mass 100,000 daltons. The K _m values of the enzyme for the substrates lactose and o-nitrophenyl--d-galactopyranoside (ONPG) are 16.7 mM and 4.4 mM, respectively, indicating, its low affinity for the substrates. The Ouchterlony immunodiffusion method exhibited immunological homogeneity of the enzyme preparation. The catalytic site of the enzyme does not take part in antigen-antibody reaction.     

A re-examination of the Na+-independent binding of [3H]β-alanine to rat brain stem-spinal cord

The Na⁺-independent binding of [³H]-alanine to rat brain stem plus spinal cord was reinvestigated, in order to study in more detail the characteristics of previously described -alanine binding processes. Binding was absent when amino acid-free postnuclear supernatants or crude synaptic membranes were used. Experiments performed with several other Na⁺-free preparations showed a sole binding component, irrespective of the preparation used. Biochemical characterization of this Na⁺-independent binding, using frozen/thawed/washed synaptosomal-mitochodrial fractions, showed that binding reached a plateau between 7 min and 13 min, increasing thereafter. Binding was linear with fraction protein over a range of 200–415 g/ml incubation medium. Binding was completely inhibited by glycine, alanine, -aminobutyric acid, -aminoisobutyric acid, hypotaurine and strychnine, and to a lesser extent by 2,2-dimethyl--alanine, brucine and gelsemine. It was insensitive to taurine, -aminobutyric acid (GABA), 2-guanidinoethanesulfonic acid (GES), carnosine, and bicuculline methiodide. Binding was reversible, saturable (K _D 20 M), and heat sensitive.     

Proteolytic specificity of chicken cathepsin L on bovineβ-casein

The proteolytic specificity of chicken cathepsin L was studied using bovine -casein as substrate. The peptide mixtures obtained after various times of hydrolysis were separated by RP-HPLC and ten peptides were identified. Chicken cathepsin L accepts proline residues in all positions except P ₁ . Looking at the amino acid residues on the amino side of the scissile bond we found three times the Tyr-Pro pair at P ₁ –P ₂ positions and that the S ₁ subsite can interact with modified amino acids such as phosphoserine.Abbreviations RP-HPLC reverse phase high performance liquid chromatography - NMec N-methyl coumarylamide - TEA triethylamine - TFA trifluoroacetic acid     

Immobilization of enzymes on alumina by means of pyridoxal 5′-phosphate

A number of proteases have been immobilized on alumina in a two-step procedure: the first step converted them into semisynthetic phosphoproteins which, in the second step, spontaneously bonded to alumina through their phosphate function. The immobilized enzymes thus obtained showed the physical properties typical of the inorganic carrier and a high activity on low molecular weight substrates.     

Effects of auxin and gibberellin on conidial germination and elongation of young hyphae in a cyclic 3′:5′ adenosine monophosphate-dependent protein kinase mutant of Neurospora crassa

The possibility that plant growth regulators may relate to a cyclic 3:5 adenosine monophosphate (cAMP)-dependent protein kinase through the control of cAMP level in the conidial germination process of Neurospora crassa was examined using a cAPM-dependent protein kinase mutant (cpk mutant) which is thought to be cAMP-independent because of defect in the regulatory subunit of cAMP-dependent protein kinase. IAA, 2,4-D and GA₃ promoted conidial germination and elongation of young hyphae in the mutant as well as in the wild-type. The result suggests that the effects of auxin and gibberellin on germination and hyphal elongation are not mediated by cAMP.     

A model for gramicidin A′-phospholipid interactions in bilayers

A model is proposed for the effect of gramicidin A on the order and structure of phospholipid dispersions. According to this model, the addition of gramicidin A influences the surrounding lipids via two independent mechanisms. The first arises from a drop in surface pressure for those lipids substantially bounded by gramicidin A. The second mechanism arises from the increase in the phospholipid headgroup spacing due to the small polar region of the polypeptide. The model provides an explanation for the currently available NMR, X-ray diffraction and Langmuir monolayer results. The model also suggests mechanisms for the ability of gramicidin A to trigger a transition of the lipid from the lamellar to hexagonal II phase, the dependence of this transition on the lipid chain length and the formation of a lamellar phase with lysophosphatidylcholine.Abbreviations NMR nuclear magnetic resonance - DMPC dimyristoylphosphatidylcholine - S molecular order parameter - CSA chemical shift anisotropy - DPPC dipalmitoylphosphati-dylcholine - LPC lysophosphatidylcholine