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The Influence of Normal and Cancer Blood on Tyrosinase Activity in vitro^*

Walter Marx

(From the William G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena, and the Emery Tumor Clinic, Los Angeles, California)

The effects of normal and cancer blood on the aerobic oxidation of tyrosine in the presence oftyrosinase were investigated as a test of malignancy, as recently suggested by Hirshfeld et al. (I). No unequivocal distinction between normal and malignant sera was possible under the experimental conditions proposed by these investigators. The reason for the disagreement between their results and those reported above is not known. Stadie et al. recently also reported a series of experiments in which the effects of normal andcancer sera on the tyrosinase system were studied, precisely following Hirshfeld's procedure (12). Essentially in agreement with our findings, these authors observed no correlation between malignancy and inhibition of the tyrosinase activity. When, however, in the results reported above, the average values of larger groups of experiments were considered, a small but statistically significant difference between the effects of normal and cancer sera was observed in one of three series, and a slight, if not significant, trend in the same direction was noted in a second group. In view of these observations, attempts were made to improve the reliability of the method by varying experimental conditions.

The experimental variations concerned: (1) the physical conditions, such as temperature, light, shaking, etc.; (2) the enzyme preparation; (3) the substrate; (4) the reaction medium (buffers, inorganic salts); (5) the blood sample. An unequivocal distinction between normal and cancer blood was not possible under any of the experimental conditions examined, although appreciably purer, more stable, and more active enzyme preparations were used.

When average values for larger groups of tests were considered, however, a trend in the direction suggested by Hirshfeld et al. was noted in several series. This trend was very small, and it was statistically significant in only 2 of 7 groups, i.e., when plasma, partially purified potato enzyme, and veronal buffer were used with tyrosine as substrate.

It is not known whether the small trend observed in some of the experimental groups is anartifact or whether it is due to a real phenomenon obscured by interfering factors of an unknownnature.

^* Supported by a grant from the Emery Cancer Research Fund.

Present address: Department of Biochemistry and Nutrition, University of Southern California, Los Angeles 7, California.