[Thermal stability study of yolk extenders for the cryopreservation of semen]

Investigated was the fate of proteins in some yolk extenders--NN (Nagasse--Niva), GH18 (after Kichev), Zr (after Zlatarev), and ZhGTs (after Milovanov)--following heat treatment. Centrifugation at 14 000 rpm of untreated extenders (NN, GH18, Zr, and ZhGTs was found to lead to the strong drop of proteins of the start with NN and GH18, whereas there was no change in the proteins of the start with Zr and ZhGTs. The heat denaturation of the four extenders at 55 degrees C, 60 degrees C, and 65 degrees C for 30 min. and their centrifugation at 14 000 for 40 min. resulted in the change of proteins--most strongly expressed with the proteins of the start and those immediately in front of it with Zr and ZhGTs. The changes in the protein macromolecules of the four extenders were best expressed at the heat denaturation for 30 min. at 70 degrees C. The densitometric profiles were strongly simplified with Zr and ZhGTs, at which first group proteins (of the front) completely disappeared. NN and GH18 changed but slightly. Second and third group proteins of NN and GH18 showed high stability as against the remaining proteins. With Zr and ZhGTs most stable proved the proteins of the second group. The strong drop of the percent share of the start proteins of NN and GH18 and the disappearance of first group proteins of Zr and ZhGTs was associated with essential denaturation changes that affected adversely the structure of protein macromolecules.