MODULATION OF SIALIC ACID-BINDING PROTEINS OF RAT UTERUS IN RESPONSE TO CHANGING HORMONAL MILIEU

A group of sialic acid binding (SAS) agglutinins has been isolated fro m the rat uteri at different stages [Proestrus (P), estrus (E) and die strus (D)] of estrous cycle. Studies of biochemical properties indicat e that SAS agglutinins are glycoprotein in nature having molecular wei ghts between 28-31 Kd and microheterogenous pI. Function-based charact erization revealed that inspite of the fact that all three proteins ex hibit sialic acid binding property, the sialic acid binding affinities , calculated from Scatchard analysis, using 4-methylumbelliferyl siali c acid as a ligand, varied in stage specific manner (Ka:D-SAS-9.03 x 1 0(5) M(-1), P-SAS-2.33 x 10(5) M(-1), E-SAS-2.13 x 10(5) M(-1)). Circu lar dichroism spectra of these three agglutinins suggested that differ ences exist in the secondary structures of the proteins isolated from different stages. Removal of carbohydrate moiety by trifluoromethane s ulfonic acid treatment and CNBr cleavage studies showed some homology between these proteins, however, the variation in the carbohydrate moi ety was apparent from the sugar analysis data. Functionally and immuno logically these proteins can be grouped as estrogenic and progestogeni c SAS agglutinins.