Comparison between crab hepatopancreas and rat liver uroporphyrinogen decarboxylase

CHAUFAN G.,; CORVI M.,; ARMESTO A.,; SAN MARTIN DE VIALE L. C.,; LUQUET C.,; RÍOS DE MOLINA M. C.

COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART B, BIOCHEMISTRY & MOLECULAR BIOLOGY.

Elsevier Science Inc

Año: 2002 vol. 133 p. 251 - 256

1096-4959

We characterised Uroporphyrinogen decarboxylase (UroD) (E.C. 4.1.1.37) in hepatopancreas of the crab Chasmagnathus granulatus as a first step to establish this enzyme as a possible biomarker for environmental contamination. We performed a comparative study of crab UroD with the enzyme UroD present in Wistar rat liver, which is known as a useful indicator of intoxication by polihalogenated aromatic hydrocarbons (PHAs). The final products were the same in crab and rat UroD: the remaining substrate (8-carboxyl-porphyrinogen), the final product Coproporphyrinogen (4-COOH) and intermediate compounds with 7-, 6- and 5-COOH. The elimination of the second carboxyl group seems to be the rate-limiting step in this multiple decarboxylation, because large amounts of 7-COOH porphyrinogen are accumulated. The Vmax/Km ratio was 100 fold higher for rat liver UroD than for crab hepatopancreas UroD, suggesting a higher efficiency of the rat enzyme. Optimum pH for enzyme activity was 7.2 and 6.8 for crab and rat, respectively. Although both systems showed the same optimum temperature (47 ºC), the activation energy was clearly different, 51.5 kJoules/mol for C. granulatus and 5.4 kJoules/mol for Rattus norvegicus (Wistar strain). Superdex 75 gel chromatography yielded a single symmetrical peak with an apparent molecular mass of  48 ± 3 kDa for crab hepatopancreas UroD, suggesting the existence of  only one enzymatic species in C. granulatus.