Competitive kinetics of sugar active transport in snail intestine.

Everted intestinal rings of the snail Cryptomphalus hortensis accumulate labelled sugars against a concentration gradient. The active transport of D-galactose (KT = 3.6 mM) is competitively inhibited by D-glucose (Ki = 8.2 mM) and by 3-0-methylglucose (Ki = 24 mM), but it is not affected by L-arabinose, D-fructose, L-arabinose and D-mannitol penetrate into the tissue at the same rate, they do not develop accumulation gradient, and all of them follow the kinetics of a diffusion process. D-glucose, on the contrary, like galactose, penetrates much more quickly and accumulates against a gradient.