= Menaquinone
A <menaquinone> is a <Vitamin K> compound with a methyl-substituted quinone ring system and an unsaturated side chain built from <isoprene>-derived units. The family includes <menaquinone-4>; the number in MK-4 counts side-chain units, not the number of <Vitamin K> <molecules>. The side-chain chemistry distinguishes <menaquinones> from <phylloquinone>.<PubChem Compound database by National Center for Biotechnology Information>[Menaquinone entries; compare menaquinone-4 and phylloquinone structures]{ref}
<Menaquinone-4> need not arrive in a tissue as the finished compound. In 2010, reducing <UBIAD1> expression in human <cells> decreased conversion of isotope-labelled <Vitamin K> derivatives to labelled <menaquinone-4>; expressing <UBIAD1> in insect <cells> supplied complementary evidence for the biosynthetic <enzyme>. The product was checked by <nuclear magnetic resonance>.<Identification of UBIAD1 as a novel human menaquinone-4 biosynthetic enzyme by Kimie Nakagawa and others>[Abstract and Figures 2–3; knockdown, heterologous expression and deuterium NMR]{ref}
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