Location of amino acid and carbohydrate transport sites in the surface membrane of normal and transformed mammalian cells

Abstract

Amino acid and carbohydrate transport in normal and malignant transformed hamster cells was studied after binding of the protein Concanavalin A (Con. A) to the surface membrane. Experimental conditions were used so that a similar number of Con. A molecules were bound to both types of cells. The transport of amino acids was inhibited after Con. A binding in the transformed cells but not in normal cells. This was found with the metabolizable amino acidsL-leucine,L-arginine,L-glutamic acid, andL-glutamine, and with the non-metabolizable amino acids cycloleucine and α-aminoisobutyric acid. Transport ofD-glucose andD-galactose was more inhibited by Con. A in transformed than in normal cells, and in both types of cellsD-glucose was inhibited more thanD-galactose. The inhibition by Con. A on transport was specific, since there was no effect on the transport ofL-fucose in either normal or transformed cells. Con. A also did not effect the entry of 3-0-methyl-D-glucose.These observations can be used to locate amino acid and carbohydrate transport sites in the surface membrane in relation to the binding sites for Con. A. The results indicate that Con. A sites are associated in normal cells with transport sites forD-glucose and to a lesser extentD-galactose, and in transformed cells with transport sites for amino acids and to a greater extent than in normal cells withD-glucose andD-galactose. Malignant transformation of normal cells therefore results in a change in the location of amino acid and carbohydrate transport sites in the surface membrane in relation to the binding sites for Con. A.