[Hexamere purine nucleoside phosphorylase from Escherichia coli K-12. Kinetic analysis and mechanism of reaction].

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.

[Hexameric purine nucleoside phosphorylase II from Escherichia coli K-12. Physico-chemical and catalytic properties and stabilization with substrates].

Some properties of hexameric purine nucleoside phosphorylase II (EC 2.4.2.

[Genetic analysis of Escherichia coli K-12 mutants defective for the structural and regulatory genes for second purine nucleoside phosphorylase].

Two types of mutants lacking the second purine nucleoside phosphorylase (PNPase 2) activity were isolated using the Escherichia coli K-12 pndR strains with constitutive or inosine-inducible synthesis of the PNPase 2. The mutations of the first type are recessive to the pndR+ allele on the F' episome. They are closely linked to the original pndR+ mutations and therefore affect the pndR gene encoding the activator protein.

[Isolation of the hexameric form of purine nucleoside phosphorylase from E. coli. Comparative study of trimeric and hexameric forms of the enzyme].

The presence of two forms (high and low molecular weight ones) of purine nucleoside phosphorylase II (purine nucleoside: orthophosphate ribosyltransferase, EC 2.4.2.

[Regulator mutants for the synthesis of a 2d purine nucleoside phosphorylase in Escherichia coli K-12. II. Mapping and study of the dominance of pndR mutations].

The synthesis of a second purine nucleoside phosphorylase (PNPII) in the wild type strains of Escherichia coli K-12 is induced by xanthosine. Three types of pndR mutants were studied, which are altered in regulation of PNPII synthesis: 1) constitutive, 2) inducible by nucleosides of hypoxantine and adenine as much as by xanthosine and 3) defective in synthesis of PNPII. All pndR mutations are located in transductional crosses on 51 min of E.

[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].

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.

[Escherichia coli K-12 mutants assimilating adenine via a new metabolic pathway].

Two pathways of adenine utilization are only known in Escherichia coli K-12: the conversion to adenosine monophosphate by adenine phosphoribosyltransferase (apt gene) and ribosylation to adenine nucleosides by purine nucleoside phosphorylase (deoD gene). The purine auxotrophs defective in synthesis of inosine monophosphate de novo (pur) and carrying apt and deoD mutations cannot satisfy their purine requirements by exogenously supplied adenine or adenosine. We have selected spontaneously secondary-site revertants (designated adu) of pur apt deoD mutants, by plating on adenine or adenosine as the sole purine source.

[Phenotypic manifestation of the pnd mutation, which promotes purine nucleoside cleavage by Escherichia coli K-12 cells, in the genome of strains defective in the metabolism of nucleic acid precursors].

Strains of Escherichia coli K-12 containing both pnd1 mutation, rendering bacteria capable to catabolize purine nucleosides without participation of purine nucleoside phosphorylase (pup gene), and mutations in several genes of purine metabolism or nucleosides catabolism have been constructed. The introduction of the deletion mutation in adenosine deaminase gene (add) into the pup pnd genome does not affect the ability of mutants to utilize adenosine and deoxyadenosine as the sole carbon and energy sources. Mutations affecting purine phosphoribosyltransferases (hpt and gpt) block the ability of pup pnd mutants to utilize hypoxanthine, guanine and their deoxyribonucleosides and also xanthine and xanthosine as the only purine source.

[Plasmid characteristics of naphthalene and salicylate biodegradation in Pseudomonas putida].

The object of this work was to study the physico-chemical and biological properties of DNAs of the biodegradation plasmids NAH and SAL. A comparative analysis of the physico-chemical parameters for these DNAs made it possible to detect a number of identical properties in them: the same sedimentation profile for covalently-closed circular DNA forms, 68--70 S; the molecular weight of ca. 50 MD; a roughly equal number of fragments (up to 23) was found when the DNAs of NAH and SAL were restricted by EcoRI endonuclease.

[Phage pf16 interrelationships with Pseudomonas putida bacteria. I. Unstable transductants and mutants of Pseudomonas putida PfG1 resistant to phage pf16].

The frequencies of transduction of the chromosomal genes by pf16 in Pseudomonas putida PgG1 are dependent on the marker transduced and unpredictable. Histidine and isoleucine-valine positive transductants, which are resistant to pf16, have been selected in the crosses with low (about 10(-8) for phage units) frequencies of transduction. Some of these transductants carry new mutations.

[Escherichia coli K-12 mutants capable of catabolizing purine nucleosides in the absence of purine nucleoside phosphorylase].

Strains of Escherichia coli K-12 defective in purine nucleoside phosphorylase (pup gene) formed on the medium with inosine as the source of carbon and energy phenotypical reversions for the ability of utilizing inosine as source of carbon or purines. The phenotypical suppression of the purine nucleoside phosphorylase deficiency is the result of the mutations (called pnd), which are mapped on the chromosome of E. coli beyond the region of the structural pup-gene location and have phenotypic manifestation distinct from that of pup+ allele: a) pnd mutants divide into some groups for the ability of utilizing several purine nucleosides, including xantosine that cannot be metabolized by pnd+ strains of E.

[Mutations of resistance to 2,6-diaminopurine and 6-methylpurine that affect adenine phosphoribosyltransferase in Escherichia coli K-12].

Independently obtained mutations (apt) of resistance to DAP (2,6-diaminopurine) and MP (6-methylpurine), that affect adenine phosphoribosyltransferase (APRT) in Escherichia coli, are different in their effect on the conversion of several substrates of APRT, such as DAP, MP, MAP (6-methylaminopurine) and adenine, to their nucleotide derivatives. Most of mutants were resistant to DAP and MP, unable to utilize MAP (as purine source) and differed in their ability to uptake adenine from the medium. Among the mutants capable to utilize adenine the following types are found: (1) resistant to DAP and MP, but capable of utilizing MAP, and (2) resistant to DAP, capable of utilizing MAP, but sensitive to MP.

[Genetic control of Escherichia coli K-12 strains' assimilation of 2,6-diaminopurine as a purine source].

Mutations of the resistance to 2,6-diaminopurine (apt), which affect adenine phosphoribosyltransferase, fail to permit the growth of Escherichia coli pur mutants (purine auxotrophs which cannot make inosine monophosphate de novo) on the medium with 2,6-diaminopurine (DAP) as the sole source of purines. Addition of a small amount of hypoxantine, but not guanine, stimulated the growth of mutants of pur apt and pur apt+ genotypes on the medium with DAP. The utilization of DAP as purine source in the presence of hypoxantine is blocked by mutations guaC (guanosine monophosphate reductase), add (adenosine deaminase) and pup (purine necleoside phosphorylase), suggesting that DAP are utilized via purine nucleoside phosphorylase and adenosine deaminase.

[Phenotypic manifestation of mutations involving resistance to 2,6-diaminopurine (apt) in the genome of purine auxotrophs of Escherichia coli K-12].

Strains of Escherichia coli K-12 containing various combinations of pur (de novo synthesis of purines), pup (purine nucleoside phosphorylase), add (adenosine deaminase) and apt (adenine phosphoribosyl transferase) mutations have been constructed. The apt mutation blocks the ability of strains of pur add and pur add pup genotype to utilize both adenine and adenosine as sole purine sources. Exogenously supplied histidine (that blocks conversion of AMP to guanine nucleotides) does not reduce the growth rate of the strain of pur apt genotype on adenosine as the sole purine source.

[Genetic study of Escherichia coli K-12 mutants resistant to 2,6-diaminopurine].

Mutants, resistant to the inhibitory effect of 2,6-diaminopurine and incapable of utilizing adenine as a purine source, are obtained from purinenucleoside phosphorylase-defective purine-dependent Escherichia coli K-12 strains. The mutations obtained (apt) disturb the uptake of adenosine and inosine only in the presence of a mutation for purinenucleoside phosphorylase (pup gene) in the genome of purine-dependent bacteria. The introduction of pup+ allele into the genome of mutants obtained (genotype purDpup apt) results in the restoration of the ability to uptake adenine and purine ribosides.