scholarly journals Electron-transport pathway of the NADH-dependent haem oxygenase system of rat liver microsomal fraction induced by cobalt chloride

1979 ◽  
Vol 178 (2) ◽  
pp. 323-329 ◽  
Author(s):  
Y Hino ◽  
S Minakami
Keyword(s):  
Cytochrome C ◽  
Rat Liver ◽  
Microsomal Fraction ◽  
Cytochrome B5 ◽  
Transport Pathway ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Haem Oxygenase ◽  
Reported Data ◽  
Nadph Cytochrome C Reductase

The hepatic microsomal haem oxygenase activity of rats treated with CoCl2 was studied kinetically by measuring biliverdin, the immediate product of the reaction. Biliverdin was extracted with diethyl ether/ethanol mixture, and was determined by the difference between A690 and A800. The apparent Km value for NADPH (at 50 microM-haematin) was about 0.2 microM when an NADPH-generating system was used, whereas that for NADH was about 630 microM. Essentially the same Vmax. values were obtained for both the NADH- and NADPH-dependent haem oxygenase reactions. No synergism was observed with NADH and NADPH. The NADH-dependent reaction was competitively inhibited by NADP+, with a Ki of about 10 microM. The inhibitoin of the NADH-dependent reaction by the antibody against rat liver microsomal NADPH-cytochrome c reductase was essentially complete, with a pattern similar to that of the NADPH-dependent reaction. The immunochemical experiment and the comparison of the kinetic values with the reported data on isolated NADH-cytochrome b5 reductase and NADPH–cytochrome c reductase indicated the involvement of the latter enzyme in NADH-dependent haem oxygenation by microsomal fraction in situ.

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

1990 ◽  
Vol 270 (3) ◽  
pp. 659-664 ◽  
Author(s):  
T Yoshinaga ◽  
Y Sudo ◽  
S Sano
Keyword(s):  
Cytochrome C ◽  
Kinetic Study ◽  
Maximum Velocity ◽  
Incubation Mixture ◽  
Biliverdin Reductase ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Haem Oxygenase ◽  
Biliverdin Ix ◽  
Nadph Cytochrome C Reductase

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.

Sign in / Sign up

Export Citation Format

Share Document