RESUMO
Barnase, an extracellular ribonuclease produced by Bacillus amyloliquefaciens, belongs to a family of small microbial ribonucleases with similar structure and properties. These enzymes hydrolyze phosphodiester bonds on the 3' side of guanosine nucleotides in RNA. The guanylic specificity of barnase is more pronounced in the hydrolysis of dinucleotides or cyclonucleotide phosphates as substrates than in the hydrolysis of RNA or polynucleotides. To have an insight into the molecular basis of this phenomenon, we mutated amino acid residue Ser-57 in the "base recognition loop" of RNase Ba. The mutant protein was expressed in Escherichia coli producing system and purified for the study of the kinetic properties in the cleavage polynucleotide reactions. It was shown that the mutation of amino acid residue Ser-57 for Ala in the "recognition loop" of RNase Ba does not significantly influence the kinetic parametres of hydrolysis of polynucleotide substrates.
Assuntos
Alanina/genética , Mutação , Ribonucleases/genética , Serina/genética , Sequência de Aminoácidos , Proteínas de Bactérias , Sequência de Bases , Hidrólise , Cinética , Dados de Sequência Molecular , Conformação Proteica , Ribonucleases/química , Especificidade por SubstratoRESUMO
A detailed analysis of noncovalent interactions in the RNase A molecule was carried out. For this purpose, contact maps based on structural data were constructed. Three hydrophobic nuclei and five microclusters were identified, and their quantitative parameters were calculated. The contacts between amino acid residues of the active center and the hydrophobic nuclei were established. The distribution of the charged amino acid residues on the of RNase A surface was shown. The data obtained was discussed in the context of the ribonuclease A family. The substitutions seen from the alignment of amino acid sequences in the family might have influence on the spatial structure of different parts of RNase A and their mutual orientation and, consequently on the biological activity of family members.
Assuntos
Proteínas/química , Ribonuclease Pancreático/química , Sequência de Aminoácidos , Animais , Humanos , Dados de Sequência Molecular , Alinhamento de Sequência , Relação Estrutura-AtividadeRESUMO
A purification method for isolating homogeneous single-strand specific nuclease S1 from alpha-amyloryzin has been developed. The yield was about 16% and purification factor--9000. Nuclease S1 thus obtained was proved to be free of contaminations of any others nucleolytic enzymes. It is shown for the first time that ribo- and deoxy-dinucleosidemonophosphates are hydrolyzed by nuclease S1 to form 5'-nucleotides with pH optimum for ApA equal to 4.6.
Assuntos
Ribonucleases/isolamento & purificação , Aspergillus oryzae/enzimologia , DNA de Cadeia Simples , Oligodesoxirribonucleotídeos , Oligorribonucleotídeos , Ribonucleases/metabolismo , Especificidade por SubstratoRESUMO
Kinetic relationships of photoreduction of 4,4'-dimethyldipyridyl and 4,4'-dibenzyldipyridyl in the presence of chlorplast were studied. It was found that photoreduction leads to the establishment of photosteady state in which the rate of photoreduction is equal to the rate of dark oxidation of reduced form. Kinetics of dark oxidation of photoreduced form were investigated. The study of inhibition of photoreduction of methylviologen and potassium ferricyanide by diuron was performed. It was shown that the nature of inhibition of both reactions is completely identical. The effect of hydrogen ions concentration and gas phase composition was studied. Stabilization of low potential electron acceptors to the oxidation by molecular oxygen in the reaction of photooxidation of water is discussed.