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It is fairly common knowledge that the vitamins K are involved in blood coagulation, even if the exact mechanism is still unknown. The compounds which possess vitamin activity are both natural and synthetic, but all share the property of being substituted or modified naphthoquinones. Martius and others, since about 1958, have demonstrated that vitamin K and analogous naphthoquinones also play a role in those areas of cellular respiration known to biochemists as electron transport, which deals with the terminal events following the Krebs cycle and which is closely associated with the cytochrome enzymes. Thus, one more class of vitamin substances may be added to the list including thiamine, riboflavin, folic acid, pyridoxine, etc., which serve observable coenzyme functions.
In the past five to seven years, an entirely new class of biologically active compounds based on benzoquinone has been discovered, and a voluminous if somewhat confusing literature already exists. The original