Isoenzyme composition of human plasma monoamine oxidase in normal subjects and in fibrotic liver disease.

Hydroxyapatite column chromatography elution profile reveals characteristic differences between monoamine oxidase (MAO) isolated from normal human plasma and from patients with hemochromatosis having hepatic fibrosis. In normal plasma, the alpha form constitutes about 84% of the enzyme, with the remainder in the beta and gamma forms. By contrast, in hemochromatosis there is less alpha form (less than 40%), an additional alpha1 form (about 20%) which was eluted immediately after alpha form, increased beta form (more than 25%), and no significant difference in gamma form. When calculated on the basis of total amount per liter, hemochromatosis is characterized by elevation of beta form (3- to 10-fold) and the presence of alpha1. These results also appear to indicate that the multiple forms separated by hydroxyapatite column chromatography represent true multiplicity of human plasma MAO in vivo.