Indications for the enzymatic synthesis of 9-O-lactoyl-N-acetylneuraminic acid in equine liver.

Fractionation of horse liver homogenate by centrifugation into heavy membranes at 10,000 x g, microsomal fraction at 105,000 x g, and the supernatant revealed sialate 9-O-lactoyltransferase activity only in the latter fraction. For the enzyme assay, the various fractions were incubated with 14C labelled CMP-N-acetylneuraminic acid, N-acetylneuramimic acid and glycoconjugate-bound N-acetylneuramimic acid. Lactoylation was identified in three different TLC systems after acid hydrolysis and purification of the sialic acids in the incubation mixtures. Enzyme activity was found only in the supernatant fraction. Glycoconjugate-bound N-acetylneuramimic acid was the best substrate tested, although some lactoylation was also found when using CMP-N-acetylneuraminic acid.