[Comparative study of purine nucleoside phosphorylase from rabbit kidney, spleen, liver and embryos]. / Sravnitel'noe izuchenie purinnukleozidfosforilazy iz pochek, selezenki, pecheni i émbrionov krolika.

Homogeneous preparations of purine nucleoside phosphorylase (EC 2.4.2.1) from rabbit kidney, spleen, liver and embryos were studied. The enzyme preparations do not differ in electrophoretic mobility. The molecular weight of the enzyme obtained from various sources was determined by gel filtration on Sephadex G-150 superfine and is about 90-92 kD. The enzyme subunits are identical in terms of molecular weight, as can be evidenced from sodium dodecyl sulfate polyacrylamide gel electrophoresis (Mr approximately 31 kD). The pH optima of these enzyme preparations for guanosine and xanthosine phosphorolysis are 6.2 and 5.7, respectively. The isoelectric point of purine nucleoside phosphorylase from rabbit kidney was determined in the presence of 9 M urea and is equal to 5.55. The enzyme is the most stable at pH 7.7; it is specific towards hypoxanthine and guanine nucleosides as well as towards xanthosine, but does not cleave adenine nucleosides. The Km values for guanosine and inosine are 1.4.10(-4) M and 1.2.10(-4) M, respectively. The enzyme does not catalyze the ribosyl transfer reaction in the absence of Pi.

[Hexamere purine nucleoside phosphorylase from Escherichia coli K-12. Kinetic analysis and mechanism of reaction]. / Geksamernaia purinnukleozidfosforilaza II Escherichia coli K-12. Kineticheskii analiz, mekhanizm reaktsii.

A kinetic analysis of the phosphorolytic reaction catalyzed by hexameric purine nucleoside phosphorylase II from E. coli K-12 in the presence and absence of reaction products was carried out. The results of the kinetic analysis are consistent with a rapid equilibrium random Bi-Bi mechanism, in which a dead-end ternary (enzyme.purine base.phosphate) complex is formed.

[Hexameric purine nucleoside phosphorylase II from Escherichia coli K-12. Physico-chemical and catalytic properties and stabilization with substrates]. / Geksamernaia purinnukleozidfosforilaza II Escherichia coli K-12. Fiziko-khimicheskie i kataliticheskie svoistva, stabilizatsiia substratami.

Some properties of hexameric purine nucleoside phosphorylase II (EC 2.4.2.1) from Escherichia coli K-12 were studied. The enzyme obeys the Michaelis-Menten kinetics with respect to purine substrates (Km for inosine, deoxyinosine and hypoxanthine are equal to 492, 106 and 26.6 microM, respectively) and exhibits negative kinetic cooperativity towards phosphate and ribose-1-phosphate. The Hill coefficient is equal to approximately 0.5 for both substrates. Hexameric purine nucleoside phosphorylase II is not a metal-dependent enzyme; its activity is inhibited by Cu2+, Zn2+, Ni2+ and SO4(2-). The enzyme is the most stable at pH 6.0; it contains essential thiol groups. All substrates partly protect the enzyme against inactivation by 5.5'-dithiobis(2-nitrobenzoic acid) and heat-inactivation and, with the exception of phosphate-against inactivation by p-chloromercuribenzoate. Hypoxanthine, especially in combination with phosphate, afford the best protection against inactivation.

[Isolation of the hexameric form of purine nucleoside phosphorylase from E. coli. Comparative study of trimeric and hexameric forms of the enzyme]. / Vydelenie geksamernoi formy purinnukleozidfosforilazy II E. coli. Sravnitel'noe issledovanie trimernoi i geksamernoi form fermenta.

The presence of two forms (high and low molecular weight ones) of purine nucleoside phosphorylase II (purine nucleoside: orthophosphate ribosyltransferase, EC 2.4.2.1) was demonstrated. The high molecular weight form of the enzyme was purified, and the properties of both forms were compared. The enzyme forms were shown to differ in their quaternary structure (trimeric and hexameric), molecular weight of the native enzyme and its subunits (85,000 and 28,000 for the trimer, 150,000 and 25,000 for the hexamer, respectively) as well as substrate specificity (the trimer is specific for all major purine nucleosides, while the hexamer does not cleave adenine nucleosides). Adenosine is a competitive inhibitor of the hexameric form with respect to deoxyguanosine (Ki = 1.16 X 10(-3) M); the Km value for deoxyguanosine is 9.85 X 10(-5) M. The isoelectric point for the both forms of the enzyme in the presence of 9 M urea is about 5.5. Both forms have a pH optimum of phosphorolytic activity between 6.5 and 7.0.

[Regulatory mutants for the synthesis of a 2d purine nucleoside phosphorylase in Escherichia coli K-12. I. Synthesis inducers and the substrate specificity of purine nucleoside phosphorylase in pndR mutants]. / Reguliatornye mutanty po sintezu vtoroi purinnukleozidfosforilazy u Escherichia coli K-12. Soobshchenie I. Induktory sinteza i substratnaia spetsifichnost' purinnukleozidfosforilazy u mutantov pndR.

Restoration of the ability to catabolise the purine nucleosides in phenotypic revertants of Escherichia coli K-12 mutants defective in deoD encoded purine nucleoside phosphorylase (PNPase 1) is the result of regulatory pndR mutations for synthesis of a second purine nucleoside phosphorylase (PNPase 2). In pndR+ strains synthesis of PNPase 2 is induced by xanthosine; in pndR mutants catabolising all purine nucleosides synthesis of this enzyme is constitutive; in other pndR mutants only catabolising some of purine nucleosides, this catabolisible nucleosides, namely, deoxyinosine, deoxyadenosine as well as, in some cases, inosine and adenosine, act as inducers of PNPase 2 synthesis. In some pndR mutants with inducible PNPase 2, xanthosine is a stronger inducer, in others it is weaker, in comparison with pndR+ strains. In bacterial cells PNPase 2 catalyses the phosphorolytic cleavage of adenosine, inosine, deoxyinosine, guanosine, deoxyguanosine and xanthosine, though in crude extracts adenosine and deoxyadenosine phosphorylase activities of the enzyme are not expressed.

[Nuclease from Aspergillus oryzae, specific for single-stranded regions of nucleic acids]. / Nukleaza iz Aspergillus oryzae, spetsifichnaia k odnonitevym uchastkam nukleoinvkh kislot.

A single-stranded specific nuclease has been purified from amyloryzine obtained from the mould fungi Aspergillus cryzae. The nuclease under study resembles the enzymes described in the literature in its ability to hydrolyze single-stranded nucleic acids. However, the enzyme essentially differs from previously known nucleases in some catalytic properties, particularly in its ability for degradation of poly A. It has been shown that the enzyme also hydrolyzes the synthetic dinucleotide pTpT to mononucleoside phosphates.