Re-examination of the presence of alpha-lactalbumin in the epididymis of the rat.

Using an assay for alpha-lactalbumin in which galactosyltransferase activity was stabilized and a tissue phosphatase inhibitor was present, no evidence was found for alpha-lactalbumin-like activity in rat epididymal tissue, epididymal fluids or medium from cultured epididymal epithelial cells with either glucose or N-acetylglucosamine as acceptor. However, when assay conditions were suboptimal, apparent transfer of radioactivity to both acceptors could be demonstrated in the epididymis and other tissues. In these assays the amount of alpha-lactalbumin registered was linearly correlated to the extent of stimulation of alpha-lactalbumin added exogenously to tissue extracts as internal standards. When rete testis fluid from rats was used as source of galactosyltransferase under suboptimal conditions, no transfer to glucose was demonstrable in epididymal fluid and an apparent decreased transfer to N-acetylglucosamine could be explained by increases in (pyro)phosphatase activity. Putative alpha-lactalbumin activity in the epididymis may be an artefact of unoptimized assays.