Abstract
Abstract Nuclear membrane NADH-cytochrome c reductase resembled the microsomal reductase in its insensitivity to rotenone and antimycin A. The trypsin-resistant nature of these two activities distinguished them from the rotenone, antimycin A-insensitive activity of outer mitochondrial membranes. Furthermore, the nuclear and microsomal NADH-cytochrome b5 reductases were similar in sulfhydryl inhibition and the protection by NADH against inhibition. Cytochrome c oxidase in nuclear membranes resembled the mitochondrial oxidase in cytochrome a,a3 content and inhibition by cyanide, azide, and carbon monoxide, but was more heat labile than its mitochondrial counterpart. Nuclear tetrachlorohydroquinone oxidase activity was revealed only at higher protamine concentrations than that optimal for the mitochondrial activity. NADH oxidase activity was cytochrome c dependent, and an 8-fold higher concentration of exogenous cytochrome c was needed for maximal activity as compared to mitochondrial NADH oxidase. The nuclear NADH oxidase was inhibited by cyanide, azide, carbon monoxide, and a sulfhydryl reagent, but not by rotenone, antimycin A, and when NADH is added prior to the sulfhydryl reagent. Moreover, the NADH oxidase was more resistant to histone inhibition, but behaved similar to the mitochondrial oxidase in blockage and reversal of the inhibition by polyanions.
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