Enzymic conversion of α-oxyprotohaem IX into biliverdin IXα by haem oxygenase

Author:

Yoshinaga T1,Sudo Y1,Sano S2

Affiliation:

1. Department of Public Health, Faculty of Medicine, Kyoto University, Kyoto 606, Japan.

2. Shiga University of Medical Science, Ohtsu, Shiga 520–21, Japan.

Abstract

Conversion of four isomers of meso-oxyprotohaem IX into the corresponding biliverdin IX was attempted with a reconstituted haem oxygenase system in the presence of NADPH-cytochrome c reductase and NADPH. Only the alpha-isomer of meso-oxyprotohaem IX was converted effectively into biliverdin IX alpha, which was further reduced to bilirubin IX alpha by biliverdin reductase. Only trace amounts of biliverdins IX beta, IX gamma and IX delta were respectively formed from the incubation mixture of the corresponding oxyprotohaemin IX isomers with the complete haem oxygenase system under the same conditions. In a kinetic study, the Km for alpha-meso-oxyprotohaem IX was 3.6 microM, which was 2-fold higher than that for protohaem IX. The maximum velocity (Vmax.) of the conversion of alpha-meso-oxyprotohaem IX into biliverdin IX alpha was twice as fast as that of protohaem IX. These results demonstrate that alpha-meso-oxyprotohaem IX is an intermediate of haem degradation and it was converted stereospecifically into biliverdin IX alpha via verdohaem IX alpha.

Publisher

Portland Press Ltd.

Subject

Cell Biology,Molecular Biology,Biochemistry

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