The biosynthesis of sialic acids.

The sialic acids (1) have in common a 9 carbon carboxylic acid, neuraminic acid (Fig. l), which may be regarded as a condensation product of a 3 carbon and a 6 carbon unit. Neuraminic acid itself is not found naturally, but several Nand O-substituted derivatives are widely distributed in nature (1). Chemical (2-4) and enzymic (5-7) degradations of N-acetylneuraminic acid have shown that this substance is composed of pyruvic acid and an N-acetylhexosamine. Working with neuraminic acid aldolase, an enzyme first described by Heimer and Meyer (5), Comb and Roseman (6) made the important observation that the N-acetylhexosamine component of N-acetylneuraminic acid is N-acetyl-n-mannosamine. This compound was a product of the reversible N-acetylneuraminic acid aldolase-catalyzed reaction: