SERUM ACID RIBONUCLEASE IN MYELOGENOUS LEUKEMIA

Abstract

Acid and alkaline RNase activities in serum were measured with yeast RNA as substrate in normal subjects and leukemic patients pre- and posttreatment, and the acid/alkaline ratios of activities were 0.63 .+-. 0.08 (SD) (N, 12), 2.28 .+-. 0.82 (N, 8) and 0.60 .+-. 0.13 (N, 9), respectively. The mean value for the ratio in pretreated leukemia was significantly higher than in the other 2 groups (P < 0.01). By separating these acid and alkaline RNases from normal and leukemic sera by phosphocellulose chromatography, that acid RNase alone increased markedly in leukemic serum. From serum and leukocytes of leukemic patients, acid RNases were purified about 2000-f and 300-fold, respectively, by phosphocellulose and Sephadex G-75 chromatography. Both enzymes displayed properties nearly identical with those of normal serum and leukocytes, except that leukemic serum acid RNase had about a 2.4-fold greater affinity for polyuridylate than for polycytidylate as substrate, in contrast to normal serum acid RNase that degraded polycytidylate exclusively. Acid RNases from serum and leukocytes of leukemia showed a similar substrate preference. The high RNase levels of leukemic sera are due to excessive leakage of acid RNase into the blood stream from abnormal leukocytes.