title: Functional interactions of lipids and proteins in rat intestinal microvillus membranes.
abstract: Interactions of lipids and proteins in isolated rat intestinal microvillus membranes were examined by studying the temperature dependence of enzyme activities and of D-glucose transport in relation to the membrane lipid thermotropic transition observed by fluorescence polarization (26 +/- 2 degrees C) and differential scanning calorimetry (23--39 degrees C). Two groups of activities were defined. Enzymes of the first group, comprising lactase, maltase, sucrase, leucine aminopeptidase, and gamma-glutamyl transpeptidase, all yielded a single slope on the Arrhenius plot in the range 10--40 degrees C and did not appear to experience functionally the effects of the lipid thermotropic transition. Each activity of the second group, comprising calcium- and magnesium-dependent adenosine triphosphatases, p-nitrophenylphosphatase, and D-glucose transport, showed a change in the slope of the Arrhenius plot in the range 25--30 degrees C, corresponding to the lower region of the lipid transition. The terms "extrinsic" and "intrinsic" activities could be applied to these groups. Delipidation of the particulate p-nitrophenylphosphatase removed the discontinuity in the Arrhenius plot. Subsequent relipidation with a variety of lipids restored a break point, but the temperature corresponded to the original discontinuity (25--29 degrees C) rather than to the phase transition temperature of the exogenous lipid added.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008563:Membrane Lipids / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D008871:Microvilli / Q000378:metabolism*; D051381:Rats; D013696:Temperature; D005723:gamma-Glutamyltransferase / Q000378:metabolism
chemical_list: D008563:Membrane Lipids; D008565:Membrane Proteins; D005723:gamma-Glutamyltransferase; D009597:4-Nitrophenylphosphatase; D006026:Glycoside Hydrolases; D000251:Adenosine Triphosphatases; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D005947:Glucose