Glycorprotein biosynthesis in calf kidney glycoprotein sialytransferase activitities towards serum glycoproteins and calf Tamm-Horsfall glycoprotein

Abstract

CMP-AcNeu:glycoprotein sialyltransltransltransltransltransferase of calf kidney cortex was characterized using serum glycoproteins and Tamm-Horsfall glycoprotein, obtained from calf urine, as acceptors. Native calf Tamm-Horsfall glycoprotein showed the best acceptor properties, followed by desialylated calf fetuin and desialylated human alpha 1-acid glycoprotein exhibiting V values of, respectively, 114, 63 and 41 nmol/h per g wet wt. of kidney cortex and Km values of 0.12, 0.16 and 0.26 mM glycoprotein acceptor. Desialylated ovine submaxillary mucine appeared to be a very poor acceptor. Tamm-Horsfall glycoprotein sialyltransferase could be distinguished from serum glycoprotein sialyltransferase by competition studies. In addition the two glycoprotein sialyltransferase activities showed different distributions over the three regions of the calf kidney: the ratios of the Tamm-Horsfall to serum glycoprotein sialyltransferase activities decreased from 3.3 in the cortex to 0.8 and 0.4 in the medulla and the papilla, respectively. It was concluded that in calf kidney at least two different sialyltransferases exist. The high cortical Tamm-Horsfall glycoprotein sialyltransferases activity corresponds markedly to the origin of the urinary Tamm-Horsfall glycoprotein, namely the distal part of the kidney tubule. Inactivation of glycoprotein sialyltransferase activity by preincubation at various temperatures and during storage at 0 degree C, could be reduced by the addition of CMP-AcNeu. The possible relevance towards the in vivo sialylation of this finding is discussed.