Effects of p-chloromercuribenzene sulfonate on the uptake of D- and L-leucines in Ehrlich ascites tumor cells.

In order to ascertain the significance of the hydrophobic region in the carrier protein responsible for the D-leucine transport reported previously, the effects of p-chloromercuribenzene sulfonate (PCMBS) were investigated on the transport of D- and L-leucines in Ehrlich ascites tumor cells. The uptake of D-leucine in the presence of PCMBS was inhibited more strongly than that of L-leucine. Km values for D-leucine uptake increased with increasing concentration of PCMBS, while those for L-leucine showed only a little increase. D-Leucine uptake was restored considerably from the PCMBS inhibition by washing with buffer, whereas L-leucine uptake was only slightly affected. The inhibition of D-leucine exit by PCMBS was also higher than that of L-leucine. These results suggest that the binding site of PCMBS for the carrier protein of Ehrlich cells is involved in its hydrophobic region that would be more significant for the binding of alkyl side chain D-leucine than that of L-leucine.