Studies on resistance characteristic and cDNA sequence conservation of transferrin from crucian carp, Carassius auratus.

Transferrin (Tf) is a kind of non-heme beta-globulin with two iron ions (Fe(3+))-binding sites. To prove Tf's physiological functions, Fe(3+)-proteins, serum iron contents, and total iron-binding capabilities were tested for Tfs of crucian carps (Carassius auratus) and sliver carps (Hypophthalmichthys molitrix). The above results demonstrated that sliver carps shared 1/3 Tf alleles with crucian carps; Tf of crucian carps had stronger Fe(3+)-binding ability and transportation ability in plasma than that of sliver carps. In addition, the results of oxygen consumption experiments indicated that crucian carps had the higher oxygen utility rate than sliver carps. For acute hypoxia exposure assay, normoxic gas mixture, hypoxic gas mixture A, and hypoxic gas mixture B were used to induce oxygen-regulated gene expression of crucian carps in acute hypoxia. The results of quantitative real-time PCR revealed that mRNA levels of Tf gene, Tfr gene and ATPase gene were down-regulated in acute hypoxia but mRNA level of LDHa gene was up-regulated in acute hypoxia. The results of crucian carp Tf-cDNA sequence analysis showed that cDNA regions of two Fe(3+)-binding sites were T(747)-T(1026) and T(1737)-A(1884) based on the principle of bioinformatics. The sequence conservation of two Fe(3+)-binding sites was higher than that of the other five regions, which were confirmed according to the subregion model of Tf-cDNA sequence.