Rat liver mitochondrial polynucleotide phosphorylase

Resisting a genetic identity: the black Seminoles and genetic tests of ancestry

In July 2000, the Seminole Nation of Oklahoma passed a resolution that would effectively expel a significant portion of its tribal members. The resolution amended the Nation's constitution by changing its membership criteria. Previously, potential members needed to show descent from an enrollee of the 1906 Dawes Rolls, the official American Indian tribal rolls established by the Dawes Commission to facilitate the allotment of reservation land. The amended constitution requires possession of one-eighth Seminole Indian blood, a requirement that a significant portion of the tribe's membership cannot fulfill. The members of the Nation who fail to meet this new membership criterion all have one thing in common: they are black.

Descendents of former slaves who came to live among the Seminole Indians of Florida in the seventeenth and eighteenth centuries, the black Seminoles have been officially recognized by the U.S. government as members of the Seminole Nation of Oklahoma since 1866.

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.

Polynucleotide phosphorylase can participate in decay of mRNA in Escherichia coli in the absence of ribonuclease II

In a mutant strain defective in polynucleotide phosphorylase, under conditions where the enzyme becomes limiting, it is possible to demonstrate that chemical as well as functional half lives of mRNA become longer if the strain is also missing ribonuclease II. These results allow to unify in a simple model a variety of observations about turnover of RNA in a variety of bacteria.

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.