THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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(ÞPRL' NIH-P-B3) , and all qther hormone preparat,ions were
kindly supplied by the NIA¡4DD of Èhe NIHTUSÀ.
Proteih Measurement
Protein concentrations of, the fractíons coLl-ected
during purification r¡rere estimated by measuring the absorbance
aE 278 nm, nraking the assumption that one unit of absorbance
was equivaJ-ent to protein concentratíon of I mg/ml. For more
accurate determinations, the protein content of the origina3_
crude extract, and of the pools containing opL at. different
stages of purification were estimated by the method of lowry
(Lowry et al ,l-951) using bovine serum albunin(BSA) as
standard. The final purified product was weighed after lyophiJ.izationf
and its protein content. per unit weight was
determined by spectrofluorometer (Aminco-Botrman), using
ovine prolact.in (NIH-P-S-l0) as st,andard¡ excitation was at
278 nm and emission at 350 nm.
Concentratioh of volumê by ultrâfiltrat,ion
A1I concentration procedures were carried out at
4C in an Amicon Diafto celL of varíous capacity ( 10,60, 4SO,
and 2,000 mI). The size of celtused. dependedon the initiat
volume required to concentrate and the final volume which
was desired. UM-Io membrane fiLters.were used in all concen-
tration steps.