Characterization of an XXXX -dependent haem-degrading system in ox heart mitochondria.

@entity2125 @entity12931 @entity274 @entity4674 @entity8864 @entity1110 @entity9050
We report the identification of an @entity2125 -dependent haem-degrading system in ox heart mitochondria. The activity was localized to the mitochondrial inner membrane, specifically associated with complex I ( @entity2125 : @entity12931 oxidoreductase). The mitochondrial @entity2125 -dependent haem-degradation activity was highly effective and displayed a rate nearly 60% higher than that of the microsomal activity. The following observations suggested the enzymic nature of the activity: (i) haem degradation by complex I did not proceed upon exposure to elevated temperature and extremes of pH; (ii) it displayed substrate specificity; (iii) it was inhibited by a substrate analogue; and (iv) it showed a cofactor requirement. Moreover, the activity was distinctly different from the @entity9050 -mediated haem-degradation activity. Also, complex I differed from the microsomal @entity1110 : @entity4674 (P-450) reductase inasmuch as the formation of an effective interaction with the microsomal haem oxygenase could not be detected. Addition of purified haem oxygenase to complex I neither influenced the rate of haem degradation nor resulted in the formation of @entity8864 alpha. In contrast, addition of haem oxygenase to @entity1110 : @entity4674 (P-450) reductase enhanced the rate of haem degradation by nearly 8-fold, and more than 60% of the degraded haem could be accounted for as @entity8864 alpha. The haem-degrading activity of complex I appeared to involve the activity of @entity274 , as the reaction was inhibited by nearly 90% by catalase, and propentdyopents were detected as reaction products. Intact haemoproteins such as @entity4674 and myoglobin were not effective substrates. However, the haem undecapeptide of @entity4674 was degraded at a rate equal to that observed for haem. Haematohaem was degraded at a rate 50% lower than that observed for haem. It is suggested that the @entity2125 -dependent haem-degradation system may have a biological role in the regulation of the concentration of respiratory haemoproteins and the disposition of the aberrant forms of the mitochondrial haemoproteins.
