Catalytic facilitation by diffusion of adsorbed substrate on membrane surface.
Membrane-alkaline phosphatase shows greater velocity of reaction than solubilized enzyme at low substrate concentration, whereas at saturation-concentration the opposite is true. The catalytic rate enhancement with the membrane-enzyme, when substrate availability is limiting, is attributed to non-specific adsorption of substrate to the membrane followed by its surface-diffusion to the active site resulting in an enhanced collision rate for the substrate with the enzyme. Experimental evidence for the adsorption-diffusion is provided by the dynamic quenching of 1-anilino-naphthalene-8-sulphonate, a membrane-bound probe's fluorescence by the substrate, 4-nitrophenyl-phosphate.
D000327:Adsorption; D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D004058:Diffusion; D007421:Intestine, Small / Q000201:enzymology; D007700:Kinetics; D008081:Liposomes; D008563:Membrane Lipids / Q000502:physiology; D051379:Mice; D008871:Microvilli / Q000201:enzymology*; D011510:Proteolipids / Q000378:metabolism; D013050:Spectrometry, Fluorescence
D008081:Liposomes; D008563:Membrane Lipids; D011510:Proteolipids; C020485:proteoliposomes; D000469:Alkaline Phosphatase