Preparative free solution isoelectric focusing of human erythrocyte uroporphyrinogen I synthase in an ampholyte pH gradient.

A free solution electrofocusing method for uroporphyrinogen I synthase (EC 4.3.1.8) in an Ampholine pH gradient on a preparative scale is described. Partial purification of the enzyme was achieved in a 4-h focusing run. Enzyme activity was found in the pH range of pH 5.1 to pH 7.0. Complete separation of the most basic and most acidic isozyme from the control and the acute intermittent porphyria (AIP) patient was obtained in this single-step procedure. The level of enzyme activity has been shown to be reduced to about half the normal value in erythrocytes of two patients from a family with AIP. A shift of maximal activity toward the acidic side of the pH gradient was observed with the abnormal enzyme. In contrast to the normal isozyme set with seven isozyme bands, the fluorescence of the three basic bands and the second acidic band was greatly reduced, whereas the intermediate forms showed increased fluorescence intensity.