Abstract
Intact and Triton disrupted mitochondria incorporate [ 14C]nicotinamide into [ 14C]NMN and [ 14C]NAD. Dialyzed Triton extracts lose this activity. The ability to form [ 14C]NMN is restored by addition of a fraction of boiled mitochondrial extract or of NMN. PRPP and ATP are not required for [ 14C]NMN formation. The specific activity of [ 14C]NMN formation decreases with serial washing of mitochondria while that of an outer membrane enzyme (kynurenine-3-monooxygenase) remains about constant. These finding suggest that the previously reported synthesis of NMN and NAD by mitochondria may be due to exchange reactions catalyzed by active glycohydrolase(s) in contaminating microsomes.
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