Cultured human synovial cells secrete hyaluronic acid (HA) into the culture medium. Glucosamine-6-3H was shown to be a direct and relatively specific precursor of HA-3H by the following observations: the susceptibility of nondialyzable radioactivity in the medium to hyaluronidase, its migration with hexuronic acid on zone electrophoresis in polyvinyl chloride, its exclusion from Sephadex G-200, and the localization of radioactivity to glucosamine after hydrolysis of the labeled polysaccharide. The presence of intracellular HA-3H was established by sequential extraction of labeled cells and by radioautography of synovial cell cultures digested with hyaluronidase in situ. When cells were exposed to medium lacking glucose, glucosamine-3H-uptake was enhanced; and this made possible electron microscopic radioautographic studies. These studies demonstrate the early and continued presence of HA-3H within the Golgi apparatus.

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