Isolation and biochemical properties of four forms of glycosylated porcine prolactin.
Four isoforms of glycosylated prolactin (G-pPRL) were isolated from porcine pituitary glands by affinity chromatography and concanavalin A-Sepharose, based upon differences in their affinity for the lectin. Structural analysis indicated differences in the carbohydrate units of the four G-pPRLs. N-glycanase treatment cleaved the oligosaccharide from the G-pPRLs, establishing N-linked glycosylation. The binding of G-pPRLs to receptors from lactating rabbit mammary glands was only 3-8% that of nonglycosylated pPRL (NG-pPRL). The immunological crossreactivity of the G-pPRLs varied from 36 to 65% that of NG-pPRL. When tested in the pigeon crop sac bioassay, G-pPRLs were only 11-40% as active as NG-pPRL. The metabolic clearance rate of one of the G-pPRLs was slower and another faster than that of NG-pPRL. We conclude that there are several forms of G-PRL of variable immuno- and bio-potencies in the porcine pituitary, and that the current radioimmunoassay for the hormone does not measure the actual bioactivity.
Sinha
Y N
YN
Whittier Institute for Diabetes and Endocrinology, Scripps Memorial Hospital, La Jolla, CA 92037.
DePaolo
L V
LV
Haro
L S
LS
Singh
R N
RN
Jacobsen
B P
BP
Scott
K E
KE
Lewis
U J
UJ
D000818:Animals; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D010856:Columbidae; D015180:Electrophoresis, Gel, Two-Dimensional; D006031:Glycosylation; D008297:Male; D008657:Metabolic Clearance Rate; D010902:Pituitary Gland / Q000737:chemistry; D011388:Prolactin / Q000737:chemistry / Q000302:isolation & purification*; D011863:Radioimmunoassay; D051381:Rats; D013552:Swine
D011388:Prolactin