THE ALBUMIN OF THE BROWN TROUT (SALMO-TRUTTA) IS A GLYCOPROTEIN

The albumin from an Atlantic salmonid, the brown trout (Salmo trutta), is 1730 Da higher in molecular mass than the albumin from a Pacific s almonid, the chinook salmon (Oncorhynchus tshawytscha), at 65 230 Da. Digestion with neuraminidase revealed that purified brown trout albumi n contained sialic acid while chinook salmon albumin did not. Concanav alin A-sepharose affinity chromatography was used to purify a glycopep tide from a total tryptic digest of brown trout albumin. The mass of t his glycopeptide (3815 Da) was determined by mass spectrometry, and th e sequence largely confirmed by N-terminal sequencing. The identified sequence of IAHCC<(NQ)under bar>SYSM-, contains an Asn-Gln-Ser glycosy lation site and is identical to residues 475-485 derived from the cDNA of the albumin from the Atlantic salmon, the closest relative of the brown trout. Glycosylation of albumin is very unusual, and has not bee n identified in either reptilian or mammalian albumins. The finding of a glycoalbumin in salmonids, ancient members of the teleost fish subc lass, coupled with evidence of albumin glycosylation in the oldest ver tebrates, agnathans, as well as amphibians, suggests that albumin was originally a glycoprotein, but lost this modification sometime between the divergence of amphibians and reptiles. (C) 1998 Elsevier Science B.V. All rights reserved.