THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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growth-promoting ef,fect, whereas cleavage of only one bond
did not Lead to any loss of activity. Símilarly, Neri et
aI (1972) observed a reduction of Lactogenic activity in the
pigeon crop-sac assay onJ-y when both disulfide bonds of hpL
were cleaved. Aubert et al (1974) have observed a good
correlation between rnolecular conformation of hpl and its
biotogic activíty vrhen they used derivaÈives that still
contained the ent,ire primary structure but had undergone
some chemical modif icat,iont toss of tertiary structure was
accompanied by J.oss of activity. However, these results
conflict vrith those of another group (Aloj et al, 1972;
Handwerger et al , 1972; Sherwood et al , Lg72r, vrho selectively
disrupted the disulfide bonds, simultaneously destroying
a methionine and a síngle tryptophan. residue, and found that
this treatment did noÈ affect the 1actogenic activity of
hPI,. Hovrever, it,s immunological potency was considerably
di¡ninished. These investigators concluded that, since the
three-dimensional structure of hpI, did not appear to be
necessary for its lactogenic activity, this effect must
reside in a small portion of the polypeptide chain. In support
of this hypothesis, they found that çy¡¡6q¿¡ bromide trêatment or pérfor;nic
acid digest of hpl retained lactogenic activity. Other studies
in which hPL has been enzymatically cleaved also suggest that.
partial hydrolysis of the hormone does not destroy its
biological activity. Neri et al (I9?2) denonstrateil that
tryptic digestion of four hpl. bonds leads to only 30t loss
of lactogenic actiyity and no reduction in somatotropic activity.