Pyridine nucleotide metabolism in Escherichia coli. III. Biosynthesis from alternative precursors in vivo

In Escherichia coli, the nicotinamide moiety of pyridine nucleotides may be derived from de novo synthesis of the pyridine ring or through the uptake of either nicotinic acid or nicotinamide. De novo synthesis is the least preferred pathway; it is suppressed if an exogenous source is available. Nicotinamide is kinetically preferred over nicotinic acid; the data are consistent with the hypothesis that nicotinamide can pass through the bacterial membrane much faster than can the charged nicotinic acid, and once inside the cell, the amide is efficiently converted to the acid.