Partial purification and properties of guinea-pig liver polynucleotide phosphorylase

Enzymatic activities in thylakoid membranes, which form medium [32P]NDP and [32P]ATP from 32Pi. Polynucleotide phosphorylase and adenylate kinase

Soluble chloroplast coupling factor 1 (CF1) and the ATP synthase complex, under uncoupled conditions, can form bound ATP from tightly bound ADP and medium Pi. This partial reaction is a powerful probe of the mechanism of ATP synthesis. During our study of the synthesis of bound ATP by CF1 other enzyme activities, which generate [32P]nucleotides from 32Pi, were characterized and controlled. Two enzymes present at significant levels in the preparations are polynucleotide phosphorylase and adenylate kinase. Polynucleotide phosphorylase (PNPase) was found both in thylakoid and CF1 preparations and catalyzed the formation of [beta-32P]ADP via its Pi----ADP exchange activity. The formation of [beta-32P]ADP during net photophosphorylation is attributable to adenylate kinase action on the [32P]ATP formed since hexokinase and glucose effectively block its production. In addition, PNPase also degraded RNA present in thylakoid preparations yielding all four [32P]nucleoside diphosphates. PNPase was also shown to catalyze a Pi----ATP exchange that is dependent on RNA primers and other cofactors.

Comparative biochemistry of the guinea-pig: a partial checklist

A great deal is known about guinea-pig biochemistry, but the information is scattered and difficult to assemble. The guinea-pig also possesses a number of unusual biochemical features which add to its interest. For these reasons we have compiled a list of biochemical characteristics of the guinea-pig, organized in a series of tables, with brief discussions of some of the entries.

Partial purification and properties of rat liver mitochondrial polynucleotide phosphorylase

1. Polynucleotide phosphorylase was partially purified from the inner membrane of rat liver mitochondria. 2. The partially purified particulate enzyme catalyses phosphorolysis of poly(A), poly(C), poly(U) and RNA to nucleoside diphosphates. 3. It is devoid of nucleoside diphosphate-polymerization activity. 4. Variable amounts of ADP/P(i)-exchange activity are associated with the polynucleotide phosphorylase and are probably due to a different enzyme. 5. ADP is the preferred substrate for exchange, and little or no reaction occurs with other nucleoside diphosphates, but ATP/P(i)-exchange takes place at one-third the rate observed with ADP. 6. The partially purified enzyme is free from the phosphatases found in the crude mitochondrial inner membrane, but is associated with an endonuclease activity and some adenylate kinase activity; no cytidylate kinase activity analogous to the latter was detectable.

A study of the localization of polynucleotide phosphorylase within rat liver cells and of its distribution among rat tissues and diverse animal species

1. Rat liver polynucleotide phosphorylase was localized in the mitochondrion, but may also occur in the nucleus. 2. The mitochondrial enzyme was found in rat heart, kidney, liver, muscle and spleen. 3. Mitochondrial polynucleotide phosphorylase is also present in calf, chicken, guinea-pig and rabbit liver and in goldfish muscle. 4. A possible physiological role for the enzyme in the control of the intramitochondrial ADP concentration is suggested.

Nucleic acid enzymology of extremely halophilic bacteria. Halobacterium cutirubrum polynucleotide phosphorylase

1. Polynucleotide phosphorylase was purified 200-fold from Halobacterium cutirubrum. 2. It is membrane-associated and can be solubilized by sonication. 3. The purified enzyme requires a high ionic strength for both stability and activity. 4. It is Mn(2+)-dependent, has all three typical polynucleotide phosphorylase activities and is specific for nucleoside diphosphates. 5. The enzyme is of low molecular weight.