Hyaluronic Acid synthesis in Rooster Comb. Effect of Testosterone on Nucleotide Sugar Metabolism

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Abstract
Enzymes involved in the synthesis of UDP-glucuronic acid (UDP-GlcUA) and UDP-N-acetylglucosamine (UDP-GlcNAc), the nucleotide sugar precursors of hyaluronic acid, were assayed in extracts of the mucoid layer of combs of normal roosters, castrated roosters (capons) and capons treated with testosterone. UDP-glucose (UDP-G) dehydrogenase and UDP-GlcNAc pyrophosphorylase activities were found to be present in extracts of both normal and capon comb. Although UDP-G pyrophosphorylase activity could be demonstrated in extracts of normal combs, it was impossible, initially, to demonstrate this activity in capon extracts. A deficiency of this enzyme would result in less UDP-GlcUA available for the synthesis of hyaluronic acid. A protein inhibitor of this enzyme was found in capon extracts which inhibited the activity of the enzyme from normal comb. Glucose 1-phosphate (G1P) was found to overcome this inhibition. By increasing the G1P or UTP concentrations in assays of UDP-G pyrophosphorylase in capon comb extracts, it was then possible to demonstrate enzyme activity. It is proposed that one mechanism by which testosterone may stimulate the synthesis of hyaluronic acid in capons is via an increased production of G1P in amounts sufficient to overcome the action of the inhibitor of UDP-G pyrophosphorylase. UDP-GlcNAc, at high concentrations, was found to inhibit the activity of fructose-6-phosphate-L-glutamine amidotransferase. Thus, in capon comb, if hyaluronic acid synthesis is inhibited initially by a lack of UDP-GlcUA, due to the inhibitor of UDP-G synthesis, eventually level of UDP-GlcNAc would rise and, by inhibiting the amidotransferase, decrease its own biosynthesis.

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