Studies on the function of vitamin A in mucopolysaccharide biosynthesis

Abstract

An in vitro system of rat colon segments and of rat colon homogenates was elaborated, which incorporated [ 35S]sulfate and [ 14C]glucose into mucopolysaccharide. Mucopolysaccharide was identified by paper chromatography and paper electrophoresis along with chondroitin sulfate carrier; by co-precipitation and dialysis with chondroitin sulfate; by hydrolysis and identification of labeled sulfate or labeled glucosamine. The homogenate system required adenosine triphosphate, diphosphopyridine nucleotide, glucose and glutamine. The level of incorporation was lowered to about one-half in colon segments and homogenates from vitamin A-deficient rats. Vitamin A, vitamin A-aldehyde and vitamin A-acid (but no other fat-soluble vitamin tested) restored incorporation to normal. With graded levels of vitamin A added, a maximum of incorporation was reached to 10 μg/6 mg of protein in the homogenates. Using glucosamine or galactosamine instead of glucose and glutamine, or uridine diphosphate acetylglucosamine, uridine diphosphate glucuronic acid, uridine diphosphate glucose and acetylglucosamine, incorporation of labeled sulfate was still dependent on vitamin A. This fact shows that the vitamin may be required either in the polymerisation reaction of the uridine derivatives, or the activation or transfer of sulfate. It was shown that the vitamin A-destroying enzyme lipoxidase can lower or abolish incorporation into mucopolysaccharide.