title: Transferrin receptors of isolated rat seminiferous tubules bind both rat and human transferrin.
abstract: The binding and uptake of rat and human transferrin by isolated rat seminiferous tubules was studied. During the isolation and incubation of the tubules, the blood-testis barrier remained intact. Iron-saturated and iron-free (apo-) transferrin use the same binding sites on the surface of the tubules, but the dissociation constant is about two times higher for apotransferrin than for iron-saturated transferrin. The affinity of the receptors is equal for rat and human transferrin, but human transferrin binds to more surface binding sites (2.6 X 10(10) per 10 cm tubule length) than rat transferrin (1.1 X 10(10) per 10 cm tubule length) at 0 degrees C. At 33 degrees C equal numbers of human and rat transferrin molecules are taken up (about 8 X 10(10)) per 10 cm tubule length. The quantitative difference between 0 degrees C and 33 degrees C is caused by the fact that at 33 degrees C receptor-mediated endocytosis and recycling occur. As a consequence, both surface and intracellular transferrin receptors are detected at 33 degrees C. The dissociation constants are not temperature-dependent.
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D051381:Rats; D011990:Receptors, Transferrin / Q000378:metabolism*; D012671:Seminiferous Tubules / Q000166:cytology / Q000378:metabolism*; D013045:Species Specificity; D013329:Structure-Activity Relationship; D013737:Testis / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*
chemical_list: D001059:Apoproteins; D011990:Receptors, Transferrin; D014168:Transferrin; C028284:apotransferrin