Differences in the Thermostability and Subunit Species of Cytochrome c Oxidase among Tissues

Cytochrome c oxidase associated with the mitochondrial innermembrane of the overground or underground organs of mung beanwas more stable at 40–55?C than that of the correspondingorgans of pea. In both plants, the enzyme in the overgroundorgans was more resistant to heat inactivation than that inthe underground organs. When the enzyme was solubilized andpartially purified from mung bean hypocotyls or roots, the enzymebecame more labile and was stabilized by exogenous phospholipid.The enzyme partially purified from mung bean hypocotyls wasmore resistant to inactivation than that from its roots eitherin the presence or absence of phospholipid. A subunit (subunitVa) of cytochrome c oxidase in mung bean hypocotyls differedimmunologically from that in the roots. We propose that at leastin mung bean, a nuclear-encoded subunit of cytochrome c oxidaseis synthesized tissue-specifically, which may cause the differencein the thermostability of the enzyme. (Received August 7, 1988; Accepted August 22, 1988)