The distribution of nucleode polymerases it calf thymus fractions.

The distribution of desoxyribonucleic acid (DNA) and ribonucleic acid (RNA) within cells of various organs has been extensively studied and the subject has been reviewed recently (l-3). On the other hand the information concerning the localization of nucleodepolymerases (4) is very limited. Ribonuclease (RNase) has been reported in chicken erythrocyte nuclei (5) and in mitochondria of rat liver cells (6). The distribution of desoxyribonuclease (DNase) has been studied by Mazia (7) in the developing sea-urchin embryo and by Neff (8) in thymus. Lang and coworkers (9, 10) have announced that kidney nuclei prepared by an undisclosed procedure contained most of the DNase of that tissue. During the past decade several attempts have been made to determine the level of DNase in different tissues (1 l-13), in the hope that it might be correlated with the ability of the tissue to grow or to regenerate. All measurements were made at pH 7.0 and many of them in the presence of Mg. Recently Siebert, Lang, and Corbet (10) reported that optimum pH values of DNase activity of different organs vary considerably. Preceding Siebert et al. by 2 years, Maver and Greco (14-16) found that extracts prepared from thymus for the purpose of studying cathepsins depolymerized both RNA and DNA. Maver and Greco noticed that the DNase activity of their extracts, measured by the liberat.ion of acid-soluble phosphorus (17) as well as by the viscosimetric technique (18), had an optimum at pH 4.5. They also noticed that the DNase of thymus was inhibited instead of accelerated by Mg ions, that it was activated by cysteine, and that it had a different thermostability curve from that of DNase from pancreas (19). The RNase activity of their extracts showed an optimum at pH 5.0 and a different thermostability curve from that of RNase from pancreas (20). Maver and Greco (16) concluded that “intracellular nucleases” (nucleodepolymerases of thymus) differ from the pancreatic enzymes. The present work was undertaken for the purpose of studying the distribution of nucleodepolymerases within the cell of calf thymus. To