THE NATURE AND CLINICAL SIGNIFICANCE OF HUMAN SERUM RIBONUCLEASE MEASURED BY USE OF SYNTHETIC SUBSTRATE

Abstract

The nature of human serum ribonuclease (RNase) measured by use of synthetic substrate (Poly C) was evaluated and non-specificity of elevated serum RNase as a pancreatic tumor marker was discussed. The optimal pH at 37°C was at 6.5 in 0.1M phosphate-borate buffer as described by Reddi, et al., but the optimal pH was at 7.4 in 0.1M Tris-HCl buffer. The serum RNase was thermostable in both conditions. The optimal pH and its activity was changed depending upon the cation, for example Na⁺ and polyamine (spermidine), in the assay system. The serum RNase activity at the superoptimal pH 7.4 in 0.1M Tris-HCl buffer showed approximately 1.5 times higher than that at the optimal pH 6.5 in 0.1M phosphate- borate buffer. This finding was found in all subjects. There was no difference in the nature of the serum RNase between normal persons and patients with pancreatic cancer.
The serum RNase activity was elevated significantly in patients with pancreatic cancer compared to normal subjects, but significantly elevated serum RNase was also seen in patients with various malignant diseases, chronic liver diseases and benign marasmic diseases. Specific elevation of serum RNase as a pancreatic tumor marker was not observed. Furthermore, it was not affected by total pancreatectomy and it changed according to the nutritional and general conditions of the patients. It was observed that the serum RNase activity of hospitalized patients was tend to correlated to a BUN/creatinine ratio in the morning fasting urine.
These clinical observations seemed to support the concept that the elevation of serum RNase activity was related to the unbalance of protein-energy metabolism in tissues or renal function.