PREPARATION AND PARTIAL STRUCTURAL CHARACTERIZATION OF ALPHA-1T-GLYCOPROTEIN FROM NORMAL HUMAN PLASMA

alpha 1T-glycoprotein (alpha 1T) was isolated from normal human plasma in the immunochemically homogeneous state. The partial amino acid seq uence and carbohydrate chains of this glycoprotein were determined. To achieve this, the carboxymethylated alpha 1T was analyzed by sequenci ng some of the lysylendoprotease, V8 protease, tryptic, and cyanogen b romide peptides as well as the N-terminal sequence of the protein. A l arge number of amino acid residues (460 amino acids) was determined by chemical procedure. The peptide sequences were compared with that of other proteins. A high degree of homology was found for proteins of th e albumin family. Further, human alpha-albumin, a new member of this p rotein family, showed an amino acid sequence identical to that of alph a 1T indicating that these two proteins are very similar in amino acid sequence and composition. These proteins are closely related to alpha -fetoprotein; however, five carbohydrate chains were found on alpha 1T at Asn12, Asn88, Asn362, Asn381, and Asn467 as biantennary complex ty pe chains and the chain on Asn362 possessed a rare consensus sequence of Asn-X-Cys. Thus, alpha 1T distinguishes itself by possessing five N -glycans, a finding reported here for the first time for the ALB famil y. (C) 1998 Academic Press.