N-Acetylglucosaminyltransferase I Activity in Bovine Ovarian Follicular Fluids from Dominant and Atretic Follicles

Abstract

The activity of α3 D mannoside 1,2 N acetylglucosaminyltransferase I (GnT I; EC 2.4.1.101), which catalyzes the first step in the conversion of oligomannose to complex or hybrid N glycans of glycoproteins, was detected in bovine follicular fluid (bFF). The GnT I activity in bFF had a pH optimum of 5.8 and an absolute requirement for either Co 2 , Mn 2 , or Mg 2 , the activity being stimulated by these cations in the above order. The apparent Km value for α1 3α1 6 mannopentaose of GnT I in bFF was 2.17 mM. The substrate specificity for the GnT I activity decreased in the following order: α1 3α1 6 mannopentaose α1 3α1 6 mannotriose α1 3 mannobiose. The GnT I activity in bFF from large atretic follicles was significantly higher than in that from large dominant follicles. Moreover there was no significant difference between the GnT I activities in bFF from dominant follicles collected before and after surge of luteinizing hormone (LH surge). These data suggest that the GnT I activity in bFF may reflect functional changes in the microenvironment which lead to follicular atresia.

N-acetylglucosaminyltransferase I Activity of Bovine Oviduct Epithelial Cells: Stimulation by Luteinizing Hormone, Vascular Endothelial Growth Factor and Tumor Necrosis Factor .ALPHA.

“…This activity can be compared with that of bovine follicular fluid (12.2 ± 2.0 nM products/h/mg protein) [5] and of rat testicular and epididymal fluids (0.23 ± 0.02 and 0 . 2 6 ± 0 .…”

“…After incubation for 24 h, the medium was collected and its GnT I activity was assayed by measuring the incorporation of [ 3 H]-GlcNAc into the acceptor substrate, α1-3α1-6 mannopentaose, as described previously [5] …”

“…Many glycosyltransferases, in their soluble forms, have been detected in testicular and epididymal fluid [4], ovarian follicular fluid [5] and uterine and oviductal fluid [6], and it has been suggested that they are involved in mammalian f e r t i l i z a t i o n [ 7 ] .…”