[Manganese-dependent ribonucleotide reductase of Propionibacterium freudenreichii subsp. shermanii: partial purification, characterization, and role in DNA biosynthesis]. / Marganets-zavisimaia ribonukleotidreduktaza Propionibacterium freudenreichii substp. Shermanii: chastichnaia ochistka, kharakteristika i rol' v biosinteze DNK.

Like Lactobacillus leichmanii, Rhizobium meliloti, and Euglena gracilis, P. freudenreichii implicates cobalamin in DNA anabolism via adenosylcobalamin-dependent ribonucleotide reductase. However, in the absence of corrinoids, P. freudenreichii is able to synthesize DNA with the involvement of an alternative ribonucleotide reductase, which is independent of adenosylcobalamin. This enzyme is localized in both the cytoplasm (80% of activity) and the cytoplasmic membrane (20% of activity), being loosely bound to the latter. Experiments with crude ribonucleotide reductase isolated from extracts of corrinoid-deficient cells showed that manganese specifically stimulates this enzyme and that it is composed of two protein subunits, a feature that is typical of all metal-containing reductases activated by molecular oxygen. Low concentrations of manganese ions enhanced DNA synthesis in corrinoid-deficient manganese-limited cells. This effect was prevented by the addition of 80 mM hydroxyurea, a specific inhibitor of metal-containing aerobic ribonucleotide reductases. It was concluded that, in adenosylcobalamin-deficient P. freudenreichii cells, DNA synthesis is provided with deoxyribosyl precursors through the functioning of manganese-dependent aerobic ribonucleotide reductase composed of two subunits.

[Effect of cobalamin derivatives on DNA synthesis in cells of Propionibacterium freudenreichii subsp. shermanii]. / Vliianie proizvodnykh kobalamina na sintez DNK v kletkakh Propionibacterium freudenreichii subsp. shermanii.

The increase of DNA-synthesis rate (according incorporation [8-14C]adenine) in B12-deficient cells Propionibacterium shermanii as a result of different cobalamines adding into the cell suspension including metoxyethyladenile analog of adenozilcobalamin and some components of vitamin B12 molecule has been found. The DNA-synthesis rate in B12-deficient cells is nearly twice lower as compared with one in B12-normal cells. Considerable stimulative effect (80-100%) was provided with coenzyme forms of cobalamin. The data confirm the participation of vitamin B12 in DNA-synthesis in Propionibacterium cells.

[DNA synthesis in relation to a varying vitamin B12 content in Propionibacterium shermanii cells]. / Sintez DNK v sviazi s razlichnym soderzhaniem vitamina B12 v kletkakh Propionibacterium shermanii.

The content of DNA in Propionibacterium cells is nearly twice as low at vitamin B12 deficiency comparing with normal cells. The rate of labeled adenine incorporation into the DNA depends on vitamin B12 content in the cells. The addition of adenosylcobalamin and thymine to the medium makes DNA content rise in the cells of the B12-deficient culture. The addition of thymine to a suspension of B12-deficient cells accelerates the incorporation of labelled adenine into DNA. The authors discuss the phenomenon of bacterial "unbalanced division" and the control of replication by changing the level of DNA precursors.

[Synthesis of organic acids by immobilized propionic bacteria in the flow system and stabilization of the process]. / Obrazovanie organicheskikh kislot immobilizovannymi propionovokislymi bakteriiami v protochnoi sisteme i vozmozhnost' stabilizatsii protsessa.

The capacity of immobilized cells of propionic bacteria to synthesize organic acids was examined. Propionibacterium shermanii cells incorporated into polyacrylamide gel were capable to synthesize propionic, acetic and pyruvic acids in the flow system. As a carbon source glucose, lactate-Na or whey lactose was used. The greatest amount of the acids was synthesized with the use of lactate-Na. The life-time of the biocatalyst (immobilized cells) can be increased by its reactivation with a nutrient medium required for optimal cell proliferation.

[Participation of methylcobalamin in the methylation of Propionibacterium shermanii DNA]. / Uchastie metilkobalamina v metilirovanii DNK Propionibacterium shermanii.

Propionibacterium shermanii is characterized by a high content of 5-methylcytosine (5 MC). The level of 5-MC in B12-deficient cells of the culture is twice as low as in the control. The in vitro treatment of DNA isolated from the B12-deficient cells with methyl-cobalamin in the presence of the extract of control cells possessing the activity of DNA-methylase increases the content of 5-MC to the control level. No additional methylation of DNA in vitro takes place in the absence of the methylase system and in the presence of other forms of corrynoids. The methylating activity is displayed either in the presence of methionine or without it. The inhibitor of methylcobalamin, i.e. diftorchlormethyl-cobalamin, blocks methylation of DNA. Small quantities of S-adenosylmethionine are necessary for the reaction of methylation.

[Determination of ribonuclease reductase activity by thin layer chromatography on ECTEOLA-cellulose]. / Opredelenie aktivnosti ribonukleotidreduktazy metodom tonkosloinoi khromatografii na EKTEOLA-tselliuloze.

A rapid and sensitive method of measuring activity of ribonucleotide reductase has been developed. The method involves separation of ribonucleotides and desoxyribonucleotides in the ECTEOLA-cellulose thin layer, elution of desoxyribonucleotides and spectrophotometric assay of eluate extinction. The method utilizes an enzyme extracted from Propionibacterium shermanii.

[Ribonucleotide reductase in Propionibacterium shermani]. / Ribonukleotidreduktaza Propionibacterium shermani

The cell-free extract of Propionibacterium shermanii was found to contain B12-dependent ribonucleotide reductase. The extract of the cells grown under the conditions of the inhibited synthesis of vitamin B12 reduces ribonucleotides with the participation of B12-independent enzyme. The synthesis of B12-dependent apoenzyme of ribonucleotide reductase is partially maintained under these conditions. Both enzymes reduce preferably ribonucleoside diphosphates. The reducing agent of nucleotides in vitro is lipoic acid or dithiothreitol, in the B12-dependent pathway, and NADPH and thioredoxin, in the B12-independent pathway. Only B12-independent ribonucleotide reductase requires Mg2+ ions. Vitamin B12 in the coenzyme form inhibits the activity of B12-independent enzyme.