Effect of light-activated benzpyrene on urease activity.

For a number of years the view has been widely held that sulfur compounds are concerned in some manner with the production of tumors by aromatic carcinogens. The best known effect of simple polycyclic hydrocarbons upon sulfur metabolism is the formation of mercapturic acids. Since previous in vestigations in this laboratory (8, 9) have shown that mercapturic acids are not present in the urine after ingestion of benzpyrene, an interference of the carcinogenic hydrocarbons with sulfur metab olism must involve some other mechanism. The dependence of a number of enzymes on free sulfhydryl groups for their activity has led to the supposition that the carcinogenic hydrocarbons might react with sulfhydryl groups of one or more enzymes controlling the growth processes. If such a reaction were of a strictly chemical nature, it should be demonstrable in vitro with all protein sulfhydryl groups, provided that the latter are on an exposed surface of the protein molecule. Ron doni and Barbieri (18), Rondoni and Bassi (19), and Gaetani (7), using cathepsin and papain prep arations, have presented results which indicate that carcinogenic hydrocarbons will inhibit the ac tion of these "sulfhydryl"-dependent enzymes. On