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Sulfhydryl Group Quantitation of Hepatoma and Liver Microsomal Fractions¹

Institute for Enzyme Research, and the Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706 [F. W. S, A. A. H, R. N. Z.], and Department of Biochemistry, Cancer Research Unit, Howard University College of Medicine, Washington, D. C. 20000 [H. P. M.]

The relationship of sulfhydryl and disulfide groups to protein synthesis in normal and rapidly growing tissues was investigated by quantitation of sulfhydryl groups in endoplasmic reticulum and polyribosomes of normal liver and hepatomas. Stripping by ethylenediaminetetraacetate and potassium chloride of normal liver smooth and rough endoplasmic reticulum reduced by 15% and increased 30%, respectively, the sulfhydryl groups available for carboxamidemethylation by iodoacetamide. This could reflect the removal of ribosomes from rough endoplasmic reticulum with the subsequent exposure of sulfhydryl groups. Exposed sulfhydryl groups of normal mature female rat liver smooth endoplasmic reticulum were decreased to a similar degree by the stripping procedure with ethylenediaminetetraacetate and potassium chloride when quantitated by either iodoacetamide or 4,4'-dithiodipyridine. This was not the case in young male and female rats, where the stripping procedure failed to decrease the exposed sulfhydryl groups of smooth endoplasmic reticulum.

An increase in the quantity of exposed sulfhydryl groups of normal young and mature rat liver rough endoplasmic reticulum after stripping by ethylenediaminetetraacetate and potassium chloride was observed with iodoacetamide. However, when 4,4'-dithiodipyridine was used, no change could be detected. The hypothesis that smooth endoplasmic reticulum arises by degranulation of the rough endoplasmic reticulum in vivo is not supported by our sulfhydryl group quantitation of smooth endoplasmic reticulum and in vitro degranulated rough endoplasmic reticulum. A negative correlation between exposed sulfhydryl groups on the polyribosomes and the rate of growth of normal liver and of Morris hepatomas 6 and 38B suggests that the conformation of the free polyribosomal proteins could be a control factor for the rate of protein synthesis. Faster growing hepatomas also have greater quantities of sulfhydryls and disulfides.

¹ This research was supported in part by grants from NIH (AM 10334 and HD 51129).

² Recipient of Grant CA 10729 from the National Cancer Institute.

Received 12/ 6/74. Accepted 3/ 7/75.