This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Colter, J. S. Articles by Ellem, K. A. O. Search for Related Content PubMed PubMed Citation Articles by Colter, J. S. Articles by Ellem, K. A. O.

The Ribonucleases of Mouse Ascites Tumors^*

J. S. Colter, Jeanne Kuhn and K. A. O. Ellem

( Wistar Institute of Anatomy and Biology, Philadelphia, Pa.)

The ribonuclease activities of seven ascites tumors of mice have been studied. Homogenates of all tumors exhibited two apparent activity optima—one between pH 4.7 and 5.4, the other between pH 8.5 and 9.3. These two values are outside the range in which normal tissues have optimal activity.

In the presence of p-chloromercuribenzoate, these two optima disappeared and were replaced by a single peak at a pH of 7.0–7.3, suggesting that the two optima seen in the absence of p-chloromercuribenzoate result from the dissociation of an enzyme-inhibitor complex.

A ribonuclease inhibitor has been isolated from Ehrlich ascites tumor cells and shown to inhibit bovine pancreatic ribonuclease. An investigation of the effect of pH on the inhibition of the crystalline enzyme by the tumor cell inhibitor has provided data which support the premise that the two optima obtained with tumor cell homogenates in the normal assay system are due to dissociation of an enzyme-inhibitor complex.

^* Supported by grants from the National Institutes of Health (C-4534 and 2G-142-C1), the American Cancer Society (E-89), and the Samuel S. Fels Fund.

Travelling Fellow of the New South Wales State Cancer Council.

Received 7/18/60.