Studies on pyridine nucleotide biosynthesis.

Until recently it had been generally accepted that the formation of diphosphopyridine nucleotide in biological systems starts from nicotinamide, with nicotinamide riboside and nicotinamide mononucleotide as intermediates (Singer & Kearney, 1954). Much of the earlier work on whether nicotinic acid or nicotinamide is the more efficient precursor of diphosphopyridine nucleotide has been controversial, but Preiss & Handler (1958a, b) unequivocally demonstrated that biosynthesis of diphosphopyridine nucleotide could also proceed by a mechanism alternative to the nicotinamide pathway referred to above, as follows: