Mammalian histidine decarboxylase; changes in molecular properties induced by oxidation and reduction.

Histidine decarboxylase from a murine mastocytoma has been submitted to different separation methods. In these experiments the activity peaks were often very broad. This heterogeneity of the enzyme is traced back to the formation of aggregates, differing in apparent molecular weight by a multiple of about 55,000, as a result of oxidation. Under non-oxidative conditions the histidine decarboxylase activity is confined to one peak in both molecular sieve chromatography, hydrophic interaction chromatography, chromatography on hydroxy apatite, pore gradient electrophoresis and electrofocusing. The molecular weight of the enzyme is estimated to be 110,000 by pore gradient electrophoresis (alkylated enzyme). The isoelectric point is pH 4.9--5.0, determined by electrofocusing under reducing conditions.