Deoxyribosyl exchange activity associated with nucleoside phosphorylase

Abrams, Richard; Edmonds, Mary; Libenson, Leon

doi:10.1016/0006-291x(65)90365-7

Cited by 21 publications

(5 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It may well be that isomeric forms of thymidine phosphorylase are involved in the two reactions. In this regard it is of interest that isomeric forms of purine nucleoside phosphorylase, an enzyme which also catalyzes direct and indirect pentosyl transfer (Abrams et al, 1965;Kim et al, 1968), have been postulated (Krenitsky, 1967).…”

Section: Discussionmentioning

confidence: 99%

Uridine phosphorylase, molecular properties, and mechanism of catalysis

Bose¹,

Yamada²

1974

Biochemistry

View full text Add to dashboard Cite

Uridine phosphorylase of the cytosol fraction of rat liver was purified to electrophoretic homogeneity. It was found to be a tetrameric protein with subunits of 26,000 molecular weight. The enzyme contained 24 half-cystine residues and 12 histidine residues. The enzyme was much less stable in Tris buffer than in phosphate buffer and new electrophoretic bands appeared after storage at -40°. Isotope exchange studies under steady-state conditions confirmed the ordered bi-bi mechanism proposed earlier (Kraut, A., and

show abstract

Section: Discussionmentioning

confidence: 99%

Uridine phosphorylase, molecular properties, and mechanism of catalysis

Bose¹,

Yamada²

1974

Biochemistry

View full text Add to dashboard Cite

show abstract

“…The enzyme has been isolated from various sources and a few of its properties have been examined in crude preparations of mammalian and avian organs and tissues, and in yeast and bacteria (Klein, 1935;Kalckar, 1947; Friedkin and Kalckar, 1950; Manson and Lampen, 1951; Heppel and Hilmoe, 1952; Korn and Buchanan, 1955;Abrams et al, 1965;Zimmerman et al, 1971;Murakami et al, 1971;Agarwal et al, 1975). Tsuboi and Hudson (1957) reported a 510-fold purification of the enzyme from human erythrocytes, and Kim et al, (1968a) reported the purification of the same enzyme to homogeneity and partial characterization.…”

Section: Guaninementioning

confidence: 99%

Bovine brain purine-nucleoside phosphorylase purification, characterization, and catalytic mechanism

Lewis¹,

Glantz²

1976

Biochemistry

View full text Add to dashboard Cite

Bovine brain purine-nucleoside phosphorylase (purine-nucleoside:orthophosphate ribosyltransferase, EC 2.4.2.1) was purified to homogeneity at a specific activity of 78 mumol min-1 mg of protein-1. A molecular weight of 78 000-80 000 was calculated for the native enzyme by fel filtration on Sephadex. Gel electrophoresis in the presence of sodium dodecyl sulfate indicated subunits of molecular weight of 38 000. Chemical and kinetic studies strongly implicated histidine and cysteine as catalytic groups at the active site of the enzyme. The pKa's determined for ionizable groups at the active site of the free enzyme were 5.8 and 8.2. Enzyme completely inactivated by p-chloromercuribenzoate was partially reactivated enzyme. A strong susceptibility to photooxidation in presence of methylene blue was observed. Photoinactivation was pH dependent, implicating histidine as the susceptible group at the active site. A rapid loss of catalytic activity upon incubation at 55 degrees C suggested heat lability. An activation energy of 9.6 kcal/mol was calculated. The nature of the catalytic mechanism of the enzyme was investigated, and initial velocity studies showed linear converging patterns of double-reciprocal plots of the data, consistent with a sequential catalytic mechanism. The product inhibition pattern was at variance with both the ordered Bi-Bi and random mechanisms. The observed competition between purine and nucleoside, and between inorganic orthophosphate and ribose 1-phosphate for this ordered mechanism, suggest a Theorell-Chance mechanism. Michaelis constants determined for substrates of the enzyme were 4.35 X 10(-5) M for guanosine, 3.00 X 10(-5) M for guanine, and 2.15 X 10(-2) M for inorganic orthophosphate.

show abstract

“…Indeed, Ott and Werkman (34) suggest that the transfer of purine and pyrimidine bases between nucleosides in E. coli is in reality a result of coupled nucleoside phosphorylase reactions. Abrams et al, (1) and Pinto and Touster (35) have provided evidence that a single enzyme in Ehrlich ascites cells catalyzes both base transfer and phosphorolytic reactions. The latter authors have shown that one activity can be converted to the other depending on the presence or absence of reducing agents such as mercaptoethanol.…”

Section: Discussionmentioning

confidence: 99%

Studies on the Pathway of Incorporation of 2-Aminopurine into the Deoxyribonucleic Acid of Escherichia coli

Rogan

Bessman

1970

J Bacteriol

View full text Add to dashboard Cite

A pathway for the incorporation of 2-aminopurine into deoxyribonucleic acid (DNA) was studied in cell-free extracts of Escherichia coli. It was demonstrated that the free base can be converted to the deoxynucleoside, and that the deoxynucleotide can be phosphorylated to the diand triphosphates and then incorporated into the DNA. From a consideration of the individual reactions in crude extracts, it is likely that the rate-limiting step in this pathway is the formation of the deoxynucleotide. Of especial interest is the observation that 2-aminopurine may be viewed as an analogue of either guanine or adenine, depending on which enzymatic step is being considered. On the one hand, it resembles guanine in that it is specifically converted from the monoto the diphosphate by guanylate kinase and not by adenylate kinase. On the other hand, it replaces adenine rather than guanine in the DNA synthesized with purified DNA polymerases. E. coli DNA polymerase utilizes aminopurine deoxynucleoside triphosphate as a substrate for DNA synthesis much better than does purified phage T5-induced DNA polymerase and is also much less inhibited by this analogue than the T5 enzyme. These experiments in vitro correlate with known differential effects of 2-aminopurine on E. coli and

show abstract

Deoxyribosyl exchange activity associated with nucleoside phosphorylase

Cited by 21 publications

References 2 publications

Uridine phosphorylase, molecular properties, and mechanism of catalysis

Uridine phosphorylase, molecular properties, and mechanism of catalysis

Bovine brain purine-nucleoside phosphorylase purification, characterization, and catalytic mechanism

Studies on the Pathway of Incorporation of 2-Aminopurine into the Deoxyribonucleic Acid of Escherichia coli

Contact Info

Product

Resources

About