Comparison of two assay methods for activities of uroporphyrinogen decarboxylase and coproporphyrinogen oxidase.

Uroporphyrinogen decarboxylase (UROD) and coproporphyrinogen oxidase (copro'gen oxidase) are two of the least well understood enzymes in the heme biosynthetic pathway. In the fifth step of the pathway, UROD converts uroporphyrinogen III to coproporphyrinogen III by the decarboxylation of the four acetic acid side chains. Copro'gen oxidase then converts coproporphyrinogen III to protoporphyrinogen IX via two sequential oxidative decarboxylations. Studies of these two enzymes are important to increase our understanding of their mechanisms. Assay comparisons of UROD and copro'gen oxidase from chicken blood hemolysates (CBH), using a newly developed micro-assay, showed that the specific activity of both enzymes is increased in the micro-assay relative to the large-scale assay. The micro-assay has distinct advantages in terms of cost, labor intensity, amount of enzyme required, and sensitivity.