HORMONE-SPECIFIC INHIBITORY INFLUENCE OF ALPHA-SUBUNIT ASN(56) OLIGOSACCHARIDE ON IN-VITRO SUBUNIT ASSOCIATION AND FOLLICLE-STIMULATING-HORMONE RECEPTOR-BINDING OF EQUINE GONADOTROPINS

Hybrid hormones were created using combinations of equine (e) LH, eFSH , and eCC alpha- and beta-subunit preparations, The efficiency of eFSH beta association was highest with eLH alpha (64-72%) and was lowest w ith eCG alpha (31-50%). Selective removal of alpha Asn(56) oligosaccha ride increased heterodimerization efficiency by 9-20% for eLH alpha, b y 21-28% for eFSH alpha, and by 28-41% for eCG alpha. Both alpha and b eta subunits contributed significantly to FSH receptor-binding activit ies of the hybrids, Purified hybrid hormone preparations consisting of either eFSH beta or eLH beta combined with eLH alpha, eFSH alpha, or eCG alpha were prepared, Equine FSH beta hybrids were more active in t he FSH radioreceptor assay than eLH beta hybrids; within each beta-sub unit group the eLH beta hybrids were the most active, followed by eFSH alpha hybrids, while the least active were eCG alpha hybrids. A trunc ated, des(121-149) eLH beta derivative (eLH beta t) combined with nati ve alpha-subunit preparations exhibited the same effect of alpha-subun it type on FSH receptor binding, Hybrids combining the eLH beta t deri vative with Asn(56)-deglycosylated (N(56)dg-)eLH alpha, N(56)dg-eFSH a lpha, and N(56)dg-eCG alpha preparations possessed 2.2- to 4.3-fold in creased FSH receptor-binding activities as compared with the same hybr id preparations possessing the Asn(56) carbohydrate., Granulosa cell b ioassay of purified native eFSH beta and eLH beta hybrid hormones indi cated no significant effect of the alpha-subunit carbohydrate differen ces on progesterone production, The alpha-subunit Asn(56) oligosacchar ide exerts a hormone-specific inhibitory influence on in vitro subunit reassociation and FSH receptor binding related to the size of its Man (alpha 1-6)Man antenna.