Mercapturic acid protein-bound

The product does not react with free cysteine but either with a protein-bound cysteine 67, 68) or with the cysteine moiety of glutathione (GSH) (69). This is followed by cleavage to the flf-acetylated free mercapturic acid. The reaction is represented by Eq. (13), where HS—R represents a bound form of cysteine. 

The sulfhydryls of cysteine, cysteine peptides including glutathione, and proteins are 1 found capable of reacting with a suitably activated hydrocarbon moiety in vitro. As described in Section VI, E, such reactions app rntly occur, though to a minor extent, in biologic sterns. When the reaction product is an S-substituted ej steine, acetylation can occur in liver or kidney mid a mercapturic acid results (Section VI, I). Similarly, hydrocarbons bound to proteins or peptides are degraded to S-substituted cysteines by metabolic activity (Section VI, H, 2). 

Further evidence for the conversion of hydrocarbon bound to protein into mercapturic acid was obtained by Smith and Wood (1959, 1963). A number of proteins were isolated from liver and intestine after administration of l ieled iodobenzene to rats. Two major fractions were obtained by electrophoresis but salt and acetone fractionation produceii a number of fractions all containing the iodophenjd group. Soluble fractions... 

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