Size heterogeneity of equine transferrin.

Abstract

It is interesting from the viewpoint of genetics, phylogeny and physiological function of transferrin (Tf), to know how the gene composition in equine Tf locus has been organized with the improvement and coming into existence of each horse breed. Accordingly, molecular weight (M.W.) differences (migrating distance), and amino acid sequences of N-terminal among Tf types and between two bands composing Tf types were analyzed biochemically to investigate at first, on construction of equine Tf locus, and to obtain phylogenetic information related to the size heterogeneity of horse Tf. The results obtained are as follows: 1) When two bands composing Tf type were analyzed by SDS-PAGE, the main component (T- component was strongly stained) was larger in M.W. than the T+ band. When this T- component was separated by isoelectric focusing, it was located on more acidic pI than T+ component. Migrating distance between T+ and T- bands in Tf·D and R types by SDS-PAGE was not changed by treatment of sugar chains with four enzymes. 2) The largest M.W. in equine Tf types was D variant (M.W. 76, 000-78, 000), followed in order by F, H2, O (M.W. 75, 000-78, 000), R (M.W. 74, 000-77, 000) and X (74, 500-76, 000 M.W.) types. 3) From the diversity of M.W. differences (migrating distance) between T+ and T- components and the degree of staining of two bands composing Tf types, equine Tf types were basically classified into three groups (D, F and H2 types, O and R types, and then X type). 4) As aminoacid sequences of N-terminal 14 residues in Tf·D, F, H2, O and R types, the T+ and T- components of Tf·D and R types were all the same, and each unique peak in Tf·D and R types fractionated by the HPLC method was evidenced that both Tf types had different amino acid sequences. From the diversity of size heterogeneity and the intensity of stained bands between T+ and T- components and among Tf types, the equine Tf type may be controlled by a few loci as haplotype rather than by single locus based on the diversity of splicing.