Photocatalyzed labeling of adipocyte plasma membranes with an aryl azide derivative of glucose.
The photoreactive glucose derivative, N-(4-azido-2-nitrophenyl)-2-amino-2-deoxy-D-glucose, has been synthesized and used as a site-directed probe to label adipocyte plasma membranes. In the absence of photoactivation, the glucose derivative was shown to inhibit D-glucose and 3-O-methyl-glucose uptake in the isolated adipocyte system. Glucose was also shown to partially inhibit the uptake of the photoreactive probe. Photolysis of this reagent with light of wavelength greater than 300 nm in the presence of intact adipose cells resulted in the covalent incorporation of radioactivity into the plasma membrane fraction. Analysis of this material by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that four membrane components were significantly labeled and that two of these components corresponded in electrophoretic mobility to the major glycoproteins with apparent molecular weights of 100,000 and 81,000. Photolysis of the glucose analog in the presence of the particulate pellet derived from homogenized adipocytes resulted in the incorporation of the radioactive label into most of the membrane proteins. Although the cells appear to be permeable to the photoreactive probe, only a few membrane components are labeled when the cells are intact, suggesting that the probe has a high affinity for these membrane components which may be functionally involved in the glucose transport system.