N-hydroxysulfosuccinimido active esters and the L-(+)-lactate transport protein in rabbit erythrocytes

Abstract

Esters of N-hydroxysulfosuccinimide strongly inhibit L-(+)-lactate transport in rabbit erythrocytes, probably by acylating amino groups on the transport protein. Lactate transport studies using bis(sulfosuccinimido) suberate (BS3), bis(sulfosuccinimido) adipate (BS2A), bis(sulfosuccinimido) dithiobis(propionate), and a variety of monocarboxylate esters suggest that an exofacial amino group of the lactate transport protein is essential for lactate transport. Also, reductive methylation studies show that even when positive charge is preserved in modified amino groups, the transport is strongly inhibited. At pH less than 6, band 3 mediated inorganic anion transport is enhanced in BS3-treated cells, while at pH greater than 6, it is inhibited. BS3-induced inhibition of L-(+)-lactate transport does not have this pH dependence. BS3 reduces the labeling of a 40-50-kDa membrane polypeptide (band R) by tritiated 4,4'-diisothiocyanato-2,2-dihydrostilbenedisulfonate ([3H]H2DIDS) and by tritiated bis(sulfosuccinimido) adipate ([3H]BS2A). Tritiated sulfosuccinimido acetate (S2[3H]acetate) also labels band R, over a range of concentrations where lactate transport is inhibited in a dose-dependent manner by S2 acetate. BS3 is a known impermeant protein cross-linker. S2 acetate permeates rabbit red cell membranes by an H2DIDS-inhibitable mechanism. BS3 cross-links the proteolytic fragments of rabbit band 3 produced by extracellular chymotrypsin. These labeling experiments support an association between band R and specific monocarboxylate transport.