J. Biol. Chem., Vol. 261, Issue 24, 11077-11085, 08, 1986
Photoaffinity labeling of the human erythrocyte glucose transporter with 8-azidoadenosine
SM Jarvis, JD Young, JS Wu, JA Belt and AR Paterson
8-Azidoadenosine was employed as a possible covalent probe of the
erythrocyte nucleoside transporter. 8-Azidoadenosine was shown to enter
human erythrocytes by a saturable mechanism (apparent Km for influx 80
microM) that was inhibited by nitrobenzylthioinosine (NBMPR), a potent
inhibitor of nucleoside transport, and competitively inhibit uridine influx
and NBMPR binding. Irradiation with UV light of human erythrocyte membranes
or a partially purified preparation of the nucleoside transporter in the
presence of [3H]8-azidoadenosine and dithiothreitol (as a free radical
scavenger) resulted in selective covalent incorporation into the band 4.5
region of sodium dodecyl sulfate-polyacrylamide gels (Mr 66,000-45,000).
Covalent labeling of band 4.5 was inhibited by adenosine, uridine, and
inosine, but NBMPR had no effect. Surprisingly, D-glucose and cytochalasin
B, but not L- glucose and cytochalasin E, blocked covalent attachment of
the ligand. No incorporation of radioactivity into membranes from rabbit
and pig erythrocytes was observed, cells which transport nucleosides
rapidly, but have little or no functional glucose carrier. Limited
treatment with trypsin of unsealed human erythrocyte membranes photolabeled
with [3H]8-azidoadenosine yielded a single radioactive fragment of Mr
19,000, a pattern identical to that obtained with [3H]cytochalasin B-
labeled membranes. These results suggest that, despite 8-azidoadenosine
being a permeant for the nucleoside transporter, under photoactivation
8-azidoadenosine preferentially labeled the glucose carrier.