Glycoprotein-sialyltransferase activity of normal human, thrombasthenic and Bernard-Soulier platelets.
Some properties of the sialyltransferase activity of homogenates prepared from normal human platelets were investigated using asialo-fetuin as substrate. The enzyme activity was optimal at pH 6.5 and was stimulated by divalent cations in the order Mg2+ greater than Mn2+ greater than Ca2+. Buffers of high ionic strength strongly reduced the activity. ATP and ADP were not inhibitors at 0.1 mM concentration, but AMP, CTP and CMP reduced the activity by 15-30%. A native endogenous acceptor for the enzyme activity was located in the platelet homogenates. The range of fetuin-sialyltransferase activity found in platelets isolated from 6 normal donors was 79 +/- 39 pmol/h/mg protein (mean +/- SD). The platelets of patients with Glanzmann's thrombasthenia and the Bernard-Soulier syndrome, which are characterized by different membrane glycoprotein deficiencies, were shown to have fetuin-sialyltransferase activities within the normal range indicating that the membrane glycoprotein defects in the platelets of these patients are not associated with the absence of sialyltransferase activity.
D000241:Adenosine / Q000494:pharmacology; D001212:Asialoglycoproteins; D001791:Blood Platelet Disorders / Q000097:blood*; D001792:Blood Platelets / Q000201:enzymology*; D002021:Buffers; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid / Q000378:metabolism; D060748:Fetuins; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007185:Incubators; D007700:Kinetics; D009438:Neuraminic Acids / Q000494:pharmacology; D009711:Nucleotides / Q000494:pharmacology; D012794:Sialic Acids / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism*; D014166:Transferases / Q000378:metabolism*; D000509:alpha-Fetoproteins / Q000378:metabolism
D001212:Asialoglycoproteins; D002021:Buffers; D060748:Fetuins; D009438:Neuraminic Acids; D009711:Nucleotides; D012794:Sialic Acids; D000509:alpha-Fetoproteins; C017029:asialofetuin; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid; D014166:Transferases; D012799:Sialyltransferases; D000241:Adenosine