The kinetic parameters of p-aminohippurate transport and activity of the alkaline phosphatase were studied using brush-border membrane vesicles isolated from the kidney cortex of normal and mutant (strain of Campbell) rats. p-Aminohippurate (PAH) transport of both normal and mutant animals was carried out by the mechanism of facilitated diffusion. The apparent Michaelis constant at 36 degrees C was equal to 7 mM, the maximal rate of PAH transport was 15 nmol/min per mg protein and the constant of inhibition by probenecid was 0.5 mM for normal rats and, respectively, 29 mM, 62 nmol/min per mg protein and 1.4 mM for mutant rats. The Arrhenius plot for the PAH transport and activity of the alkaline phosphatase showed the breakpoints at 28-30 degrees C for normal rats and at 36-38 degrees C for the Campbell strain rats. The thermotropic phase transitions detected by the EPR method with 5-doxylstearate as a probe were recorded at 21-30 degrees C and 30-35 degrees C for normal and mutant rats, respectively. Therefore, characteristic features of the PAH carrier and alkaline phosphatase activity in normal and Campbell strain rats are determined by the difference in the phase state of their membrane lipid bilayers. We suppose that mutation in the Campbell strain gives rise to a membrane pleiotropic effect which enables us to understand the mechanism of genetic control of the lipid structure and membrane fluidity.