NADHcytochrome

NADHcytochrome, sometimes described as NADH-cytochrome c reductase or NADH:cytochrome oxidoreductase, refers to a class of enzymatic activities that mediate electron transfer from NADH to cytochrome c. In many contexts, it denotes membrane-associated systems that can operate as part of or alongside the mitochondrial respiratory chain, but the exact composition and location can vary by tissue and organism.

The core reaction is the transfer of electrons from NADH to oxidized cytochrome c, typically via intermediate flavin-containing proteins or other redox partners. The overall process can be written as NADH + cytochrome c(oxidized) → NAD+ + cytochrome c(reduced). In mitochondria, the principal pathway for NADH oxidation is via Complex I of the electron transport chain; NADHcytochrome c reductase activity is often observed as an auxiliary or subsidiary route in membranes such as the inner mitochondrial membrane or endoplasmic reticulum–associated systems, where flavoprotein and cytochrome components are present.

Localization and structure of NADHcytochrome activities are heterogeneous. In mitochondria, these activities may be associated with peripheral membrane complexes or soluble flavoproteins that can interact with cytochrome c. In microsomal or endoplasmic reticulum fractions, a NADH-cytochrome b5 reductase–type system can relay electrons to cytochrome c via cytochrome b5, contributing to reductive capacity in specific cellular contexts.

Physiological relevance varies; the activity is often used in biochemical assays to probe redox state and membrane-bound electron transfer, and its importance relative to primary respiratory pathways differs across tissues. Synonyms include NADH–cytochrome c oxidoreductase and related membrane-associated reductases.