[Metabolism of rumen microbial populations formed on biosubstrates with different assimilation under the effect of pentachlorophenol]. / Metabolizm mikrobnykh populiatsii rubtsia, sformovanykh na biosubstratakh riznoï dostupnosti, za diï pentakhlorfenolu.

It has been established that metabolism of mixed microbial population formed on easy assimilated sources of energy and nitrogen (concentrate diet) progressed on higher level. There is increase of amilolytic activity, formation of lactate, ammonia, low molecular carbonic acids with predomination of propionate molar fraction. The increased resistance to effect of pentachlorophenol (PCP) is characteristic nature of the latter. The role of the most resistant synthrophic bacteria to PCP increases. The pure strains of Streptococcus bovis and Megasphaera elsdenii do not stop metabolism at 100 microM of PCP. Mixed population of microorganisms formed on hard accessible biosubstrates (cellulose) and Butyrivibrio fibrisolvens have the increased cellulosolytic activity and while the high sensibility even to low doses of PCP (10-40 microM) is observed. It has been supposed that mechanism of PCP effect is ambiguous for various species of microbial complex of rumen. It's effect strength on all main chains of metabolism (membrane transport, energetic exchange, protein biosynthesis, etc.) significantly depends on capacity of pool of metabolic intermediates formed as a result of definite program of biotechnology of nurture, but significantly decreases the harmful effect of biocides.

Human cytomegalovirus protease complexes its substrate recognition sequences in an extended peptide conformation.

Substrate hydrolysis by human cytomegalovirus (HCMV) protease is essential to viral capsid assembly. The interaction of HCMV protease and the N-terminal cleavage products of the hydrolysis of R- and M-site oligopeptide substrate mimics (R and M, respectively, which span the P9-P1 positions) was studied by NMR methods. Protease-induced differential line broadening indicated that ligand binding is mediated by the P4-P1 amino acid residues of the peptides. A well-defined extended conformation of R from P1 through P4 when complexed to HCMV protease was evidenced by numerous transferred nuclear Overhauser effect (NOE) correlations for the peptide upon addition of the enzyme. NOE cross-peaks between the P4 and P5 side chains placing these two groups in proximity indicated a deviation from the extended conformation starting at P5. Similar studies carried out for the M peptide also indicated an extended peptide structure very similar to that of R, although the conformation of the P5 glycine could not be established. No obvious variation in structure between bound R and M (notably at P4, where the tyrosine of the R-site has been suggested to play a key role in ligand binding) could be discerned that might explain the observed differences in processing rates between R- and M-sequences. Kinetic studies, utilizing R- and M-site peptide substrates for which the P5 and P4 residues were separately exchanged, revealed that these positions had essentially no influence on the specificity constants (kcat/KM). In sharp contrast, substitution of the P2 residue of an M-site peptide changed its specificity constant to that of an R-site peptide substrate, and vice versa.

Evidence of a conformational change in the human cytomegalovirus protease upon binding of peptidyl-activated carbonyl inhibitors.

A series of N-tert-butylacetyl-l-tert-butylglycyl-l-Ngamma, Ngamma-dimethylasparagyl-l-alanyl-derived inhibitors (trifluoromethyl ketone 1, pentafluoroethyl ketone, 2, methyl ketone 3, and alpha-ketoamide 4, with respective KI values of 1.1, 0.1, 2100, and 0.2 microM) of the human cytomegalovirus protease were used to study the effect of binding of peptidyl inhibitors on the intrinsic fluorescence and CD properties of the enzyme. In the presence of saturating concentrations of compounds 1, 2, and 4, an identical blue shift in the fluorescence maximum of the enzyme upon specific tryptophan excitation was observed relative to that of the free protease. In the case of the methyl ketone 3, whose inhibition of the enzyme does not involve formation of a covalent adduct as evidenced by 13C NMR studies of carbonyl-labeled inhibitors, the blue shift in the emission was also observed. For both compounds 1 and 2 which exhibit slow-binding kinetics, the observed rate constants for the slow onset of inhibition of substrate hydrolysis correlate well with the kobs values of the time-dependent change in the emission spectra. Studies employing a double mutant of HCMV protease Ala143Gln/Trp42Phe identified Trp-42 as the principal fluorescence reporter. Taken together with information provided by our recent elucidation of the crystallographic structure of the enzyme [Tong, L., Qian, C., Massariol, M.-J., Bonneau, P. R., Cordingley, M. G., & Lagacé, L. (1996) Nature 383, 272], these observations are consistent with the inhibition of HCMV protease by peptidyl ketones involving a conformational change of the protease. A mechanism involving a kon limited by dehydration of the hydrated species, followed by rapid ligand binding and a conformational change prior to covalent adduct formation, is proposed for activated inhibitors such as 1 and 2.

Solid-phase synthesis and hybridization properties of DNA containing sulfide-linked dinucleosides.

Oligodeoxyribonucleotides incorporating non-hydrolyzable dialkyl sulfide linked thymidine dimers (TsT) were synthesized chemically by the solid-phase approach. The sulfide dimer TsT was stable to degradation by snake-venom phosphodiesterase, calf spleen phosphodiesterase, Nuclease P1 and Nuclease S1. Thermal denaturation analysis indicated that the incorporation of TsT dimers into DNA weakened, but did not prevent, binding to complementary DNA and RNA over a wide range of salt concentrations (10 mM to 2 M NaCl).