A study on the nature of macroamylase complex. Dissociation of macroamylase by substrates.

Characteristics of a macroamylase that was considered not to be formed by the binding of normal amylase to immunoglobulins were studied. The macroamylase was reversibly dissociated into apparently normal amylase by treating the macroamylasemic serum with guanidine hydrochloride. Concanavalin A precipitated a large portion of the macroamylase. When the macroamylase was purified by affinity chromatography using an insoluble starch polymer at neutral pH, a considerable dissociation of the enzyme into apparently normal amylase was observed with the purified preparation. Such dissociation of the macroamylase was demonstrated by briefly incubating the patient's serum with a low-molecular weight starch, a substrate of the enzyme. This dissociated enzyme showed upon electrophoresis essentially the same isozymic pattern as that of normal serum amylase. When the patient's serum was incubated with the low molecular weight starch for a prolonged period to hydrolyze the starch completely and was dialyzed, reconstitution of macroamylase resulted. The amylase-binding substance(s) that is supposed to be involved in the formation of macroamylase was found to release when the enzyme was adsorbed on the insoluble starch polymer at 0 degrees C. The present results strongly suggest that the amylase-binding substance(s), probably polysaccharide(s) or glycoprotein(s), binds to the substrate-binding site of normal amylase to form a macroamylase complex.