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.

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