Heterogeneity of horse transferrin: the role of carbohydrate moiety

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Abstract
Homozygous horse transferrin (Tf O) is highly heterogeneous. In starch gel electrophoresis it gives at least 9 zones. Two main components (2a and 4b) were purified by rivanol and ammonium sulfate precipitation, DEAE-Sephadex chromatography and SP-Sephadex chromatography. MW of 75,200 and 80,500 for components 2a and 4b, respectively, were determined by sedimentation equilibrium ultracentrifugation. Amino acid compositions of the 2 components were similar, and there were no differences in the N-terminus (Glu followed by Gln) and the C-terminus (Val). Differences were found in carbohydrate composition between components 2a and 4b. Component 2a contained 10 mol of sugar components per mole of protein (4 hexoses, 4 hexosamines and 2 sialic acids), while component 4b contained twice the number of both total carbohydrates and individual sugar components. Carbohydrates were identified as mannose and galactose (ratio mannose:galactose .apprxeq. 1.5:1), N-acetylglucosamine and N-acetylneuraminic acid. At present it is not clear whether the difference between the 2 components resides solely in the difference of carbohydrate contents. Component 2a may have one diantennary glycan, while component 4b has 2.