Protoporphyrinogen oxidase and porphobilinogen deaminase in variegate porphyria

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Abstract
Two enzymes of the haem biosynthetic pathway were investigated in patients with variegate porphyria. Protoporphyrinogen oxidase in cultures of Epstein‐Barr virus transformed lymphoblasts from twenty‐seven patients showed a mean maximal velocity (Vmax) of 0·39 ± 0·08+ nmol of protoporphyrin mg protein‐1 h‐1, a 52% reduction (P < 0·001) from a non‐porphyric control group (0·82 ± 0·10). Km values (1·00 ± 0·27 μM) did not differ significantly (P > 0·05) from control values in any of the patients. The mean Vmax of porphobilinogen deaminase in the cultures was 1·50 ± 0·18 nmol of uroporphyrin mg protein‐1 min‐1, a 24% reduction (P < 0·001) from controls (1·94 ± 0·14). Mean porphobilinogen deaminase activity in the erythrocytes of twenty‐one patients with variegate porphyria was 8·37 ± 1·99 nmol of uroporphyrin 1 erythrocytes‐1 s‐1, a 28% reduction (P < 0·001) from normal (11·98 ± 2·11). The reduced activities of these two enzymes comply with the expression of variegate porphyria during its quiescent and acute phases.

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