Free and membrane-bound polyribosomes in normal and Rauscher-virus-infected mouse spleen cells

Detection of RNAase inhibitor from different species and organs

Human placental alkaline RNAase inhibitor was purified to homogeneity. Activity was measured after each purification step. The final identification of the purified protein was done by two-dimensional polyacrylamide gel electrophoresis and by immunoblotting. Antibodies were prepared by immunization of rabbits with the highly purified inhibitor. The availability of the antiserum directed against the human inhibitor enabled the detection of RNAase inhibitor from various other organs and species. This procedure has the advantage over the usual activity test in that the inhibitor can be found even if its activity has been lost.

Oestrogen-induced changes in the relative concentrations of ribonuclease and ribonuclease inhibitor in rat uterus

The cytoplasm of the immature rat uterus contains an excess of ribonuclease inhibitor over endogenous cytoplasmic ribonuclease. The ratio of free inhibitor to bound inhibitor is approximately 3:1. After treatment with oestrogen, there is a marked increase in the level of cytoplasmic ribonuclease such that the enzyme is present in excess of the inhibitor. The increase in activity appears to result from at least 2 distinct ribonucleases with molecular masses of approximately 14000 and 18000. The changes observed after oestrogen treatment are also evident during normal development of the rat uterus. The implications of these results on the proposed role of the inhibitor/ribonuclease system are discussed.

Polyribosome profiles and ribonuclease activity in spleens of normal and anaemic mice

The extent to which the polyribosome content in splenic extracts is affected by the level of endogenous ribonuclease activity was investigated. Ribonuclease activity, free and inhibited, was determined under ionic conditions optimal for preservation of polyribosomes. The results show that ribonuclease activity in control spleens varies mainly with the amount of ribonuclease inhibitor, indicating that free ribonuclease activity is stable. In rapidly proliferating splenic tissue the enzymatic activity is regulated by changes in both the amount of inhibitor and enzyme available. The ribonuclease versus ribonuclease-inhibitor balance was found to parallel the proportion of polyribosomes in a polysome profile.

Changes in free and membrane-bound ribosomes during the development of chick liver. A new cell-fractionation approach

A major difficulty in studying quantitative changes in free and membrane-bound ribosomes in a tissue under different physiological conditions is that membrane-bound ribosomes are not usually recovered quantitatively in a conventional microsomal fraction. This problem was resolved for developing chick liver by determining the conditions for the isolation of a microsomal fraction containing the highest practicable yield of rough vesicles, and then separating it into free-ribosome- and rough-vesicle-containing fractions. With the aid of a marker enzyme for the microsomal membranes and the RNA content of the recovered membrane-bound ribosomes, it was possible to correct for the recovery of rough vesicles and hence to determine the concentration of membrane-bound ribosomes in the homogenate. Despite the fact that morphological studies have suggested that most of the cellular ribosomes are not bound to membrane in chick liver cells at the earliest developmental age studied (6 days of egg incubation), 49% of the total ribosomes were found to be membrane-bound by using the new fractionation technique. This fraction increased (to 66%) during development. The discrepancy between the cell-fractionation and morphological approaches could not be attributed to artifacts of the separation method but rather to difficulties inherent in the morphological approach.

Myocardial aminoacyl-transfer-ribonucleic acid synthetase and aminoacyl-transferring enzyme activity

The properties of cytoplasmic aminoacyl-tRNA synthetase and aminoacyl-transferring enzymes in the myocardium were examined and methods for the assay of the activity of these enzyme systems were developed. Aminoacyl-tRNA synthetase activity was measured from the rate of incorporation of (14)C-labelled amino acid into aminoacyl-tRNA. Transferase activity was measured from the rate of incorporation of amino[(14)C]acyl-tRNA into protein in the presence of a standard preparation of hepatic ribosomes. Aminoacyl-tRNA synthetase activity is labile once the heart has been homogenized, whereas transferase activity is stable. The source of energy for synthetase activity is ATP; that for transferase is GTP. Transferase activity was inhibited by puromycin and stimulated by dithiothreitol, whereas synthetase activity was unaffected.