Thiol reagents are substrates for the ADP‐ribosyltransferase activity of pertussis toxin

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Abstract
Thiols such as cysteine and dithiothreitol are substrates for the ADP‐ribosyltransferase activity of pertussis toxin. When cysteine was incubated with NAD+ and toxin at pH 7.5, a product containing ADP‐ribose and cysteine (presumably ADP‐ribosylcysteine) was isolated by high‐performance liquid chromatography, and characterized by its composition and release of AMP with phosphodiesterase. Cysteine has a K m of 105 mM at saturating NAD+ concentration. The ability of thiols to act as a substrate is one explanation for the very high concentrations (250 mM or greater) that have been observed to enhance the apparent NAD glycohydrolase activity of the toxin.