CLONING AND SEQUENCING OF THE MONOCARBOXYLATE TRANSPORTER FROM MOUSE EHRLICH-LETTRE TUMOR-CELL CONFIRMS ITS IDENTITY AS MCT1 AND DEMONSTRATES THAT GLYCOSYLATION IS NOT REQUIRED FOR MCT1 FUNCTION

Lactate transport is mediated in most tissues by H+-monocarboxylate(-) -cotransporters (MCTs). We have cloned and sequenced the lactate trans porter from Ehrlich Lettre tumour cells by using the polymerase chain reaction (PCR) to amplify MCT1-related sequence from cDNA. The sequenc e is 93% and 87% identical to MCT1 from Chinese hamster and human resp ectively and so represents mouse MCT1. Most differences between MCT1 f rom Chinese hamster and mouse are conservative substitutions, located in hydrophilic parts of the molecule. Specific antipeptide antibodies confirm the presence of MCT1 protein in membranes from Ehrlich Lettre tumour cells. One difference between the mouse and Chinese hamster MCT 1 is the absence of a predicted external consensus sequence for N-link ed glycosylation in the mouse sequence, Using N-glycanase-F treatment and an in vitro translation system, we provide evidence that this glyc osylation site is not actually utilised in Chinese hamster MCT1. These results are discussed in relation to current understanding of the rol es of glycosylation of membrane proteins.