to determine the sidedness of the active site of n-acetyltransferase on the microsomal membranes , two s-acetyldextran polymer derivatives ( mr 500 000 ) of cysteine and n-acetylcysteine which represent an nonpermeant substrate and product for this enzyme , respectively , were examined for their effects on the vesicle-associated enzyme activity .
C0010654
cysteine
C0001047
n-acetylcysteine