Enzymatic formation of a phosphorylated derivative of vitamin K.

A role for naphthoquinones in oxidative phosphorylation has been demonstrated with a cell-free system from Mycobacterium phlei.1-3 The natural naphthoquinone of this microorganism, vitamin K9H, functions between the flavoprotein and cytochrome b on the NAD+-linked and malate-vitamin K reductase pathways.3' 4 Evidence has been presented for the existence of a phosphorylative site between the natural quinone and cytochrome b.2, 5, 6 Restoration of the quinone function has been shown to occur on supplementation with vitamin K, (I) to the quinone-depleted system.1' 2, 5