Pre-prolactin accumulates in rat pituitary cells incubated with a threonine analog.

The proteolytic processing of rat pre-prolactin (Pre-Prl) to prolactin in isolated hemipituitaries was inhibited by the threonine analog, beta-hydroxynorvaline (Hnv). Pre-Prl accumulated as a major labeled intracellular product, even during pulse labeling longer than 2 h, but it was not secreted. Inhibition of Pre-Prl processing may result from incorporation of Hnv at the Pre-Prl cleavage site. This system offers the opportunity to study the disposition of an accumulated pre-protein in cells.