Activities of acid, neutral and alkaline ribonuclease (RNase) were determined in serum of patients with actue lymphocytic leukemia (ALL) using homo-and hetero-polyribonucleotides as substrate to evaluate the substrate specificity and the mechanism of action for the serum RNases and to find out the better substate for the serum enzyme as a marker for ALL.
1. Activities of acid, neutral and alkaline RNases in serum of ALL were increased by 47%, 57% and 78%, respectively, and the positive rates of the serum enzymes as a marker for ALL were 46%, 57% and 68%, respectively.
2. All of the acid, neutral and alkaline RNases in serum of ALL were observed to cleave C-C, C-A, C-U, C-G and U-U linkages of RNA, of which C-C and C-A linkages were principal sites of cleavage by the serum enzymes. Little activity was obseryed toward the A-A and G-G linkages of RNA and double stranded RNA.
3. The positive rate of both neutral and alkaline RNases in serum as a marker for ALL exhibited the highest value when poly C was used as substrate, and the positive rate was decreased in the order of poly AC, poly CU, poly CI and poly CIU used as substrate. The positive rate of acid RNases in serum as a marker for ALL was similar to those of neutral and alkaline RNases except that the positive rate of the acid RNase measured with poly U as substrate was higher than that measured with poly AC as substrate.
4. Ratio of serum neutral and alkaline RNase activities in ALL measured with poly AC as substrate to the RNase activity measured with poly C as substrate (ratio of poly AC/poly C) and poly CIU/poly C were lower than that of normal serum RNase activity. This suggests the possibility that the nature of RNases in serum of ALL might be different from that in normal serum.
5. Six out of 9 cases of ALL studied, activity of neutral RNase in serum was decreased following the chemotherapeutic measures against ALL and returned to the normal level at the end of chemotherapy (36 weeks of chemotherapy). These results suggest that serum neutral RNase of the three types of RNases studied could be used as markers for biochemical, diagnostic and therapeutic effect and that studying the serum RNase might be important to understand the nature of the blood cancer.
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