Reactive Thiol Groups in Calf-Intestinal Alkaline Phosphatase

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Abstract
Incubation of calf intestinal alkaline phosphatase with iodoacetamide results in time-dependent changes in catalytic activity. Above 2 mmol/1, inactivation occurs but at lower iodoacetamide concentrations there is a relatively slow increase in activity. The changes induced by the treatment, i.e. both activation and inactivation, are irreversible, affect V(max) only, and are not prevented by the presence of the substrate analogue P(1). Total inactivation is associated with the incorporation of 4 mol iodoacetamide/mol of enyzme but the majority of the enzymic activity is lost after incorporation of only 1 mol of iodoacetamide. Thus any structural alterations of one subunit consequent to modification may be transmitted to the partner subunit, i.e. activity loss seems to be a cooperative process.