Control of glycoprotein synthesis. Bovine colostrum UDP-N-acetylglucosamine:alpha-D-mannoside beta 2-N-acetylglucosaminyltransferase I. Separation from UDP-N-acetylglucosamine:alpha-D-mannoside beta 2-N-acetylglucosaminyltransferase II, partial purification, and substrate specificity.