Lipid Ordering and Enzymic Activities in Chromaffin Granule Membranes

Abstract

The interaction of a variety of fluorescent probes with the membranes of [bovine] adrenal medullary chromaffin granules is described. Changes in the motional properties of the bound probes with temperature were investigated, and evidence is presented which indicates that ordering of the membrane lipids occurs below 33.degree. C. The ordering is characteristic of the membrane lipids and is retained by sonicated aqueous dispersions of the total lipid extracted from chromaffin granule membranes. The ATPase and NADH:acceptor oxidoreductase activities of the chromaffin granule membrane have discontinuous Arrhenius temperature vs. activity relationships with transitions at 33.degree. C. The ATPase has a 2nd transition at 36.5.degree. C. The 33.degree. C transition for the NADH:acceptor oxidoreductase is removed by treatment with the detergent Triton X-100. The correlation between the onset of lipid ordering and the change in activation energy of the membrane-bound enzyme activities is discussed in terms of the co-operative interactions of the different membrane components. The possible role of lipid ordering in exocytosis is discussed.