The Interaction of Soluble Proteins with Lipid Interfaces

Abstract

There is now a vast amount of evidence to show that virtually all the multi-enzyme systems which exist in cells contain phospholipids as an integral part of their structure and activity. Generally this evidence is as follows — the enzymic activity can be substantially reduced by extracting the complexes with organic solvents e.g. aqueous acetone or by treating them with phospholipases (A or C) and largely restored by reacting them with aqueous suspensions of isolated phospholipids. Often there is little specificity about the structure of the phospholipid required although it has recently been claimed that phosphatidylserine is specific for the restoration of delipidated transport ATPase (Wheeler & Whittam, 1970). There is little evidence to show precisely why the phospholipids are essential components of such enzyme complexes. Our lack of knowledge is usually covered by all enveloping general statements, such as that they act as cement substances holding the individual enzymes with their active centres orientated towards one another so that the lipid provides a medium for electron flow within complexes and between complexes. However, these explanations would not necessarily apply to the requirement for lipids by individual particulate enzyme reactions e.g. lecithin as a co-factor for D-3-hydroxybutyrate-NAD oxidoreductase (Jurtshuk, Sekuzu & Green, 1963) or acidic phospholipids for protoheme ferrolyase (Sawada, Takeshita, Sugita & Yoneyama, 1969) and here it is possible that the phospholipid may produce some activating conformation change of the enzyme protein.