| Popis: |
Summary Evidence for microheterogeneity of lamb fetuin was obtained by electrophoresis on different supports of either purified fetuin or total fetal serum. In both cases, 7–8 bands were observed corresponding to the different variants. Fetuin electrophoretic mobility slightly increases during the first two months of pregnancy and then remains constant from the 3d month until birth. During this later stage, the pHi of all the variants were found between 3.88 and 4.28 as determined by electrofocusing. Seven fractions can be resolved by CM-cellulose chromatography, each generally containing a major variant along with 2 minor ones. In all fractions, the hexose and osamine content remains constant while that of NANA gradually decreases from fraction 1 to fraction 7. However, the difference in NANA content between fraction 1 and fraction 7 does not exceed two residues per molecule and therefore cannot account for the number of variants. After neuraminidase treatment of each individual fraction, 5 to 6 bands can be observed by electrophoresis at pH 5.5. When the same treatment is applied to unfractionated purified fetuin, 7 to 8 bands are still observed. From the above results, we conclude that the variations in the carbohydrate content of lamb fetuin are insufficient to account for its microheterogeneity. We therefore postulate that structural isomerisms might also be involved in this phenomenon. |
