The effect of glucose on cellobiose uptake and β-D-glucosidase activity inStreptomyces granaticolor

Glucose inhibits the inducible synthesis of β-D-glucosidase inStreptomyces granaticolor. Neither cAMP nor cGMP influence the inhibitory effect of glucose. Glucose also inhibits the inducible synthesis of the cellobiose uptake system but has no effect on its activity. This may be the mechanism underlying glucose inhibition of induction of β-D-glucosidase inS.granaticolor.     

Partial purification and properties of Galleria mellonella larvae proteolytic inhibitors acting on Metarhizium anisopliae toxic protease

Gel permeation, preparative isoelectric focusing, and affinity chromatography were used to purify three inhibitors of proteolytic activity from perchloric acid extracts of last instar Galleria mellonella larvae. Electrofocusing experiments revealed three isoinhibitors with different isoelectric points: inhibitor I-1 with p1 of pH 5.6, inhibitor I-2, pH 7.7, and inhibitor I-3 (of small inhibitory activity), pH 8.6. By affinity chromatography on trypsin-Sepharose 4B the I-1 was purified 9.7 ×, but 71.1% of inhibitory activity was lost. Molecular mass of the inhibitory complex was 12,600 Da. I-1 and I-2 are relatively stable to heat at several pHs with minor stability at pH 10. I-1 and I-2 inhibit serine proteases about 2.5 times as much as sulfhydryl proteases. In the same ratio protease P-1 and protease P-2 from Metarhizium anisopliae are inhibited.     

Phytosociological characteristics of theRondeletio correifoliae-Andropogonetum multinervosi ass. nova (Sierra de la Siguanea,Isla de la Juventud,Cuba)

The contribution deals with the phytocenological analysis of theRondeletio correifoliae-Andropogonetum multinervosi, an endemic savanna association occuring on the Siguanea Hills (Sierra de la Siguanea) near the Colony Hotel.     

The effect of temperature on the acetylcholinesterase activity of muscle microsomes

Membrane vesicles which constitute the sarcotubular system were separated and the fraction enriched in T-tubules purified by a calcium loading procedure. The preparations of unfractioned microsomes and T-tubules have been analyzed for their relative content of enzyme markers and acetylcholinesterase. The amount of this enzyme in the T-tubule fraction was higher than in mixed microsomes but less than two-fold the value of vesicles derived from sarcoplasmic reticulum. Arrhenius plots of membrane-bound and soluble acetylcholinesterase from either mixed microsomes or fractions enriched in T-tubules show an anomalous behaviour as two break points were obtained. The first discontinuity was found at about 17 degrees C for membrane-bound, and 12-14 degrees C for soluble acetylcholinesterase. The second one being at about 25 degrees C for both particulate and detergent-solubilized enzyme. The changes in activity with temperature suggest that lipid-protein, detergent-protein and protein-protein interactions might be involved in the stabilization of the enzyme both in the natural membrane and in the soluble state.     

Streptomyces rimosus extracellular proteases 3. Isolation and characterization of leucine aminopeptidase

Summary A leucine aminopeptidase was purified to homogeneity fromStreptomyces rimosus culture filtrates, which are waste broth of oxytetracycline bioproduction process. Purification procedure includes ultrafiltration and chromatography on CM-Sephadex, AH-Sepharose and FPLC Mono S column. The enzyme is a monomer with molecular weight of 27,500 Daltons and pI of 7.3, stable in broad pH range and up to 70°C. It is a metallo enzyme dependent on Ca²⁺ ions for its full activity. By its specificity it is a true aminopeptidase active on amino acid amide, arylamide, peptide and ester bonds. The hydrolysing activity shows preference for leucine at the N-terminal position of substrates, also acts on aromatic acids and methionine, but does not release glycine, proline, acidic amino acids orD-amino acid residues.     

Study of the hydrolysis and ionization constants of Schiff base from pyridoxal 5''-phosphate and n-hexylamine in partially aqueous solvents. An application to phosphorylase b.

Formation and hydrolysis rate constants as well as equilibrium constants of the Schiff base derived from pyridoxal 5'-phosphate and n-hexylamine were determined between pH 3.5 and 7.5 in ethanol/water mixtures (3:17, v/v, and 49:1, v/v). The results indicate that solvent polarity scarcely alters the values of these constants but that they are dependent on the pH. Spectrophotometric titration of this Schiff base was also carried out. We found that a pKa value of 6.1, attributed in high-polarity media to protonation of the pyridine nitrogen atom, is independent of solvent polarity, whereas the pKa of the monoprotonated form of the imine falls from 12.5 in ethanol/water (3:17) to 11.3 in ethanol/water (49:1). Fitting of the experimental results for the hydrolysis to a theoretical model indicates the existence of a group with a pKa value of 6.1 that is crucial in the variation of kinetic constant of hydrolysis with pH. Studies of the reactivity of the coenzyme (pyridoxal 5'-phosphate) of glycogen phosphorylase b with hydroxylamine show that this reaction only occurs when the pH value of solution is below 6.5 and the hydrolysis of imine bond has started. We propose that the decrease in activity of phosphorylase b when the pH value is less than 6.2 must be caused by the cleavage of enzyme-coenzyme binding and that this may be related with protonation of the pyridine nitrogen atom of pyridoxal 5'-phosphate.     

Effect of interferon treatment on blockade of protein synthesis induced by poliovirus infection

Treatment of HeLa cells with lymphoblastoid interferon leads to a drastic inhibition of infective poliovirus. Even relatively high concentrations of human lymphoblastoid interferon HuIFN-alpha (Ly) (400 IU/ml) do not prevent destruction of the cell monolayer after most of the cells have been infected with poliovirus. Analysis of macromolecular synthesis in a single step growth cycle of poliovirus in interferon-treated cells detected no viral protein synthesis. In spite of this inhibition of viral translation, the shut-off of host protein synthesis in interferon-treated cells is apparent when they are infected both at low and high multiplicities. Although viral RNA synthesis is inhibited considerably in cells treated with interferon, a certain amount is detected, suggesting that some viral replication takes place. Analysis of membrane permeability after poliovirus infection shows a leakage to 86Rb+ ions and modification of membrane permeability to the translation inhibitor hygromycin B at the moment when the bulk of virus protein synthesis occurs. These changes are delayed and even prevented if cells are pretreated with interferon. A situation is described in which host protein synthesis is shut-down with no major changes in membrane permeability, as studied by the two tests mentioned above. Prevention of viral gene expression by inactivation with ultraviolet light of the input virus or by treatment with cycloheximide blocks the shut-off of protein synthesis. This does not occur in the presence of 3 mM guanidine. These observations are in agreement with the idea that some poliovirus protein synthesis takes place in interferon-treated cells and this early gene expression is necessary to block cellular protein synthesis.