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Human seminal transferrin (HSmT) is an iron-containing glycoprotein whose structural properties have not been adequately investigated. The carbohydrate content of the purified glycoprotein amount to 6.1%, and monosaccharide analysis revealed the major oligosaccharide moiety to be of the N-glycoside type. The carbohydrate chains were released from the iron-free form by digestion with peptide N-glycosidase F (PNGase F) in the presence of detergents such as SDS and beta-octylglucoside. After ethanol precipitation and fractionation on Bio-Gel P-6 and Bio-Gel P-2, the oligosaccharide was further purified on Mono-Q and desalted on Bio-Gel P-2. By 600-MHz 1H-NMR spectroscopy, the primary structure of the major N-linked oligosaccharide component was established to be: [formula: see text]

Denaturation of human seminal transferrin (HSmT) compared with human serum transferrin (HSrT) was followed to check structural differences between these two proteins. Second derivative UV spectroscopy indicated that treatment with 6 M guanidine hydrochloride (Gnd.HCl) induced greater structural changes in HSrT than in HSmT and, in particular; (i) the exposure value of tyrosinyl residues was almost 2.5-fold higher in native HSmT than in native HSrT; and (ii) a much more pronounced movement of tryptophanyl residues toward a higher polar environment could be noticed in HSrT after incubation with denaturing agent. Fluorescence measurements showed that: (i) a shift of the maximum emission wavelength of HSmT occurred (maximum emission was centered at 333 nm instead of 323 nm as for HSrT; excitation = 280 nm); (ii) the intrinsic tryptophan fluorescence intensity of HSmT increased after 36 hr in the range of 1.5-4.0 M of denaturant, whereas an opposite behavior was found for HSrT in the range 0.0-2.0 M; and (iii) the wavelength maximum of fluorescence emission changed in a biphasic manner for HSrT and, conversely, under the same experimental conditions, HSmT gave a linear and parallel increase of fluorescence emission after 1 and 36 hr. We can conclude that this different behavior of HSmT with respect to HSrT might be due mainly to the fact that both the number and the exposure of tyrosinyl and tryptophanyl residues are different. Lately, these effects are discussed in relationship with the fact that HSmT contains less than half disulphide bridges than HSrT.