The Lipid Dependence of Glucose-6-Phosphate Phosphohydrolase

Abstract

The functional dependence of membrane enzyme activities on the composition of the lipid bilayers with which they are associated has been studied by many techniques (1). Unfortunately, many of these techniques may alter the structure of the membrane-bound enzymes or, in the case of chemical modifications of membrane lipids or phospholipase treatment, the introduction of by-products may affect enzyme activities. Recent advances in the isolation and application of phospholipid transfer proteins permit the manipulation of membrane lipid composition in vitro under mild conditions that would not be expected to alter the structure of functional membrane proteins. One of the many lipid-dependent membrane-bound enzymes that has been studied extensively is glucose-6-phosphatase, a microsomal complex composed of a glucose-6-phosphate (Glc-6-P) carrier and of a phosphohydrolase located on the luminal membrane surface (2). In this communication we present evidence that Glc-6-P phosphohydrolase activity is altered by some modifications of the microsomal membrane lipid composition but not by others.