JBC, Vol. 251, Issue 9, 2703-2708, May, 1976
Purification and characterization of bovine placental lactogen
F. F. Bolander Jr and R. E. Fellows
Bovine placental lactogen (bPL), a polypeptide hormone functionally related
to bovine growth hormone (bGH) and bovine prolactin (bPL), has been
isolated from placentas by pH and ammonium sulfate precipitation, gel
filtration, and ion exchange chromatography on DEAE- and CM-cellulose. The
hormone has been purified to approximately 99% homogeneity, as determined
by end group analysis. On disc gel electrophoresis at pH 9.0 bPL migrates
as a pair of closely spaced bands (Rf = 09517 and 0.541) between the
positions of bGH and bPR. Its molecular weight, as estimated by gel
filtration on Sephadex G-200 in 6 M guanidine hydrochloride and 6.5 mM
dithiothreitol, is 22, 150 and its isoelectric point is 5.9. The amino acid
composition of bPL closely resembles that of bGH and bPR except for a
higher content of serine and glycine and a lower leucine content. Like bPR,
it has 2 tryptophans and 6 cysteines, but its COOH-terminal sequence is
identical with that of bGH: -Cys-Ala-Phe-OH. By Ouchterlony
immunodiffusion, bPL forms lines of partial identity with bGH against bGH
antisera and with ovine placental lactogen (oPL) against oPL antisera. In
the bPL-antibPL system, oPL forms a line of partial identity while bGH and
bPR do not cross-react. However, bPL does not form a precipitin line with
bPR antisera. These data would indicate that in terms of structure, and
hence molecular evolution, bPL and other subprimate placental lactogens
occupy a position more intermediate between growth hormone and prolactin
than do the primate placental lactogens.
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