Studies on the metabolism of pteridines in Tawa Sarcoma

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In succession to the previous studies on the pteridine metabolism in Tawa sarcoma, the metabolism in Yoshida sarcoma, which is also a transplantable malignant tumor of rat and is quite similar to Tawa sarcoma in its morphological and biological characteristices, was studied as well.High activities of both pteridine-metabolizing enzymes; sepiapterin reductase and dihydrofolate reductase were detected in Yoshida sarcoma. These activities were 4.3 times and 1.1 times higher, respectively, comparring to those activities in normal rat liver. Sepiapterin reductase was about 3 times higher than dihydrofolate reductase in the activity. Levels of these enzyme activities in Yoshida sarcoma and in the liver of host animal rose with the multiplying of ascites tumor cells and reached maximum level at the pure culture stage of ascites cells (at 5 days after inoculation).Above pecuriarities in Yoshida sarcoma were equally observed in Tawa sarcoma as shown previously except for the maximum time of activities durring cell multiplying (at 4 days after inoculation).Sepiapterin reductase in Yoshida sarcoma was found to have analogy to the enzyme in Tawa sarcoma or in normal liver in the result of partial purification and in some kinetices such as Km values (for sepiapterin and NADPH) and rates of inhibition with various pteridines, carboxylic acids and -SH inhib itors. Sepiapterin reductase in Yoshida sarcoma, like Tawa sarcoma enzyme, showed higher pH optimum (at pH 6.1) than that of normal liver enzyme (at pH 5.5). But it was peculiar that sepiapterin reductase in Yoshida sarcoma had about 10% higher reaction velocity with NADH than that in Tawa sarcoma.