Redox potentials of certain vitamins K: implications for a role in sulfite reduction by obligately anaerobic bacteria.

Redox potentials of a menaquinone (MK-6), isolated in earlier researches from two species of the obligately anaerobic genus, Desulfovibrio, as well as two other vitamins K(2)-menaquinones (MK-5) and (MK-9)- have been determined polarographically. The measurements have been validated by determination of redox potentials of 1,4-naphthoquinone and vitamin K(1) which agree with published potentiometric values. E(m7) for menaquinone (MK-6) is -0.067 +/- 0.010 V. Redox potentials calculated for terminal acceptor couples currently proposed in the mechanisms of sulfate reduction by Desulfovibrio are consistent with the involvement of menaquinone (MK-6) in at least one of the steps postulated during electron transfer with ultimate production of sulfide.