Febs Letters Volume 115, Number 1-2./Volume 116, Number 1-2. [antikvár]

Volume 128,number 2 FEBS LETTERS June 1981 June 1980 Review Letter IDENTIFYING THE MONOSACCHARIDE TRANSPORT PROTEIN IN THE HUMAN ERYTHROCYTE MEMBRANE M. N. JONES and J. K. NICKSON Department of Biochemistry, University of Manchester, Manchester, Ml 3 9PL, England Received 19 March 1980 1. Introduction Monosaccliarides permeate tiie human erythrocyte membrane by a mechanism of facilitated diffusion which has been extensively investigated [1-3], Many of the earher studies were concerned with Idnetics [4] but there is an increasing interest in identifying the membrane proteins involved in the transport process by means of reconstitution experiments in Uposomes [5-9] and planar hpid bilayers [10-14]. Fig.l shows Relative Mobility Fig.l. Electrophoretogram of human erythrocyte membrane proteins as obtained by the Laemmli procedure [30]. The notation of the bands is that of Fairbanks et al. [15]. a polyacrylamide gel polypeptide profile of human erythrocyte membrane proteins. Many very similar profiles have been reported in the literature (see below). In terms of the notation of Fairbanks et al. [15] for the designation of the polypeptide bands, band 3 and the region between bands 4.2 and 5, the so-called 4.5 region, have been proposed as components of the monosaccharide transport system. The association of band 3 with glucose transport was implicated by binding experiments [16-18] and reconstitution studies [6,11-14] whereas other investigations have led to the involvement of region 4.5 [5,7,8,19,20]. Band 3 is a heavily stained region of the electrophoretogram which contains the transmembrane polypeptides associated with anion permeability [21-24], ATPase activity [25,26] and cytochalasin B binding [17]. The structural features and disposition of the band 3 polypeptides have been investigated in some detail [27—29]. In contrast the 4.5 region is relatively lightly stained. Using the procedure in [15] for SDS-PAGE (sodium dodecyl-sulphate-polyacrylamide gel electrophoresis) this region usually consists of a number of overlapping bands whereas the Laemmli procedure [30] gives better resolution to reveal 6—7 bands [31,32] as seen in fig.l. While the bulk of the experimental evidence implicates band 3 or region 4.5, 'spectrin' (bands 1,2) has also been related to glucose transport [33]. A necessary requirement in the identification of the polypeptides involved in monosaccharide transport is that the number of such polypeptides must be sufficiently large to account for the number of transport sites in the membrane. It is thus important to accurately establish both the number of transport sites and the amounts of particular polypeptides believed to be involved in transport. WhUe these points have been Elsevier/North-Holland Biomedical Press ^^^