Reactive Thiol Groups in Calf-Intestinal Alkaline Phosphatase

Incubation of calf intestinal alkaline phosphatase with iodoacetamide results in time-dependent changes in catalytic activity. Above 2 mmol/l, 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 Vmax only, and are not prevented by the presence of the substrate analogue Pi. Total inactivation is associated with the incorporation of 4 mol iodoacetamide/mol of enzyme 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.