Heterogeneity of human liver alanine aminotransferase due to sulfhydryl groups oxidation.

The cytosolic isoenzyme of human liver alanine aminotransferase exhibited a progressive change in its chromatographic behavior on DEAE-Sepharose when partially purified preparations were stored for up to 8 days at 4 degrees C. This change was characterized by the appearance of an additional chromatographic variant and was avoided by addition of 2-mercaptoethanol. The experimental evidence presented indicates that the progressive oxidation of free sulfhydryl groups of the enzyme is responsible for the charge modifications and heterogeneity observed.