The ultracytochemical localization of cytidine-5'-monophosphatase in normal human thyroid follicle cells.

The properties and distribution of an enzyme specifically hydrolyzing cytidine-5'-monophosphate and the possible relationship of the enzyme to the synthesis and secretion of thyroid hormone in man were investigated using cytochemical methods. Activity due to cytidine-5'-monophosphatase was separated from that due to acid or alkaline phosphatase, both of which are also capable of hydrolyzing cytidine-5'-monophosphate. This distinction was established on the basis of manganese ion stimulation and differences in localization, levels of activity, and pH optimums. The localization of the enzyme along the face of Golgi apparatus involved in the formation of thyroglobulin suggests an association of the enzyme with the glycosylation of thyroglobulin.