Inhibition of fructose diphosphate aldolase by phosphatidylserine liposomes.

Phosphatides and their cleavage products modulate the activities of a variety of proteins, including glycolytic enzymes. Very abundant glycolytic enzyme fructose bis-phosphate aldolase was found to be strongly inhibited by phosphatidylinositol (PI) in the form of liposomes, which was interpreted as a result of electrostatic interaction of the protein with t h e negatively charged liposomes (Gutowicz and Modrzycka 1979). The inhibitory effect of PI was associated with quenching and batochromic shift of the protein fluorescence. More recently Koppitz et al. (1986) have shown that also water soluble inositol phosphates, which are cleavage products of phosphoinositides, act as potent inhibitor of aldolase. Thus, the inactivation by P I may result from interaction of the enzyme either with the liposomes, or with single molecules of an inhibitor present in the lipid phase. A simultaneous operation of b o t h mechanisms seems also possible. Since aldolase belongs t o membrane bound proteins (Strapazon and Steck 1976, Harris and Winzor 1990) it was of interest t o study the effect of another anionic phospholipid, phospatidylserine (PS), an important s tructural component of biological membranes. It was shown t o be a potent inhibitor of glyceraldehyde-3phosphate dehydrogenase (Gutowicz and Modrzycka 1978; Sidorowicz et al. 1990) and 3-phosphoglycerate kinase (Sidorowicz et al. 1986), but it also acts as an activator of other enzymes, e.g. pyruvate kinase (Dabrowska et al. 1988) and protein kinase C (Hannun and Bell 1986). T h e aim of the present communication was to study the effect of PS on the ac­ tivity and fluorescence of rabbit muscle aldolase. In order to show a possible effect of the lipid impurities, three different preparations of PS were examined, namely syn­ thetic dipalmitoyl PS-1, highly purified bovine brain PS-2 (both were from Sigma