Gaston de Lamirande

Autodegradation of ribonucleic acid of rat-liver microsomes

Abstract The autodegradation of the endogenous ribonucleic acid of the microsomal fraction of rat liver was studied. The results indicate that ribonuclease (ribonucleate oligotido-nucleotidohydrolase) and a phosphodiesterase (orthophosphoric diester phosphohydrolase) are present in this fraction. The former is stimulated by phosphate, arsenate and EDTA, and is inhibited by Mg 2+ whereas the latter is activated by phosphate but inhibited by arsenate and EDTA. The autodegradation of RNA reaches a plateau in the presence of phosphate or arsenate and suggests the presence in the microsomal fraction of rat liver of another enzymatic system. Chromatographic analysis of the acid-soluble products of reaction shows that the main products of degradation are oligonucleotides, and nucleosides. The absence of nucleotides in the incubation mixture is due to the presence of nucleotidases.

Intracellular distribution of 5′-ribonuclease and 5′-phosphodiesterase in rat liver☆

Abstract The intracellular distribution of 5′-ribonuclease and 5′-phosphodiesterase was studied in rat liver. Glucose 6-phosphatase and acid phosphatase were also studied as reference enzymes. The results show that the 5′-ribonuclease is essentially a mitochondrial enzyme whereas 5′-phosphodiesterase is present in the nuclear and microsomal fractions. Analysis of the degradation products of the mitochondrial ribonuclease showed that this ribonuclease yields oligonucleotides terminated by 5′-phosphate end-group.

Ribonucleases of rat liver: I. Partial purification and properties

Abstract Methods for the purification of both the acid and alkaline ribonucleases of rat liver are reported. It was possible to obtain a purified alkaline ribonuclease freed from acid ribonuclease activity. However, the preparation of acid ribonuclease was contaminated by the presence of alkaline ribonuclease activity. Some characteristics of both enzymes are reported. Preliminary results on the specificity of these enzymes showed that acid RNAase splits cyclic mononucleotides (purine or pyrimidine) whereas alkaline RNAase does not.

Studies on the intracellular and intramitochondrial distribution of a 5′-endonuclease in regenerating rat liver

Abstract 1. 1. Following partial hepatectomy, the total 5′-endonuclease activity per g of rat liver is similar to that of untreated control rats. However, an increase of 30% is observed in the liver of sham operated rats. 2. 2. The intracellular localization of the liver 5′-endonuclease is the same in normal, sham operated, and hepatectomized rats: the enzyme is mainly localized in the mitochondrial fraction. 3. 3. The 5′-endonuclease from both the sham operated and the regenerating rat livers is localized in the mitochondrial outer membrane fraction.