Studies on N-acetylneuraminic acid biosynthesis in chicken liver and hepatoma Mc-29 by using [14C]N-acetylmannosamine and [14C]glucosamine.

The biosynthesis of free N-acetylneuraminic (sialic) acid (N-acetylneuraminic + CMP-N-acetylneuraminic acid) in chicken liver and hepatoma Mc-29 by using [14C]N-acetylmannosamine and [14C]glucosamine was studied in vivo. The specific activity (SA) of hepatoma N-acetylneuraminic acid labelled with [14C]glucosamine is lower than that of liver, showing that the rate of conversion of UDP-N-acetylglucosamine to N-acetylneuraminic acid is reduced in tumor cells. The biosynthesis rate of sialic acid in hepatoma cells is higher when [14C]N-acetylmannosamine was applied. The UDP-N-acetylglucosamine-2'-epimerase activity was nearly 3-fold lower in hepatoma compared to that in liver. The time course of [14C]N-acetylmannosamine incorporation into free and protein bound sialic acid in hepatoma and liver was also showed. The SA of hepatoma protein bound sialic acid remained lower in all time points investigated. The results agree with the assumption that the metabolic pathways leading to sialic acid synthesis and to sialylation of tumor glycoconjugates are altered after malignant transformation.