Identification and partial characterization of parathyroid hormone-related protein in human and bovine milk

Abstract
Parathyroid hormone-related protein (PTHrP) was measured in human and bovine milk by radioimmunoassay (RIA) and bioassay, and the molecular forms characterized by gel chromatography and immunoblotting of affinity-purified PTHrP. Mean immunoreactive PTHrP(1–34) concentrations were 23 and 87 μg/l in human and bovine milk respectively. Bioactive (BIO) PTHrP concentrations determined by cyclic AMP production by ROS 17/2·8 cells correlated significantly (P< 0·001) with those obtained by RIA (BIO = 1·04RIA−3·4, r = 0·939). Gel filtration of human and bovine milk identified several peaks with immunoactivity and bioactivity. Immunoblotting of affinity-purified PTHrP revealed multiple molecular species including components with mobilities similar to those of PTHrP and its subfragments. These studies confirm the presence of immuno- and bioactive PTHrP in milk and suggest that post-translational processing is complex and variable. Journal of Endocrinology (1990) 127, 167–176

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