Mechanism of salt-mediated inhibition of I i poprotei n I i pase

The activity of lipoprotein lipase isolated from rat postheparin plasma has been determined with synthetic lipids, in the presence and absence of apoprotein of the natural substrate very low density lipoprotein, as a function of medium ion-pair concentration of a number of different inorganic salts. The several kinetic effects of lipoprotein protein on lipase activity were specifically and quantita- tively reversed in the presence of molar sodium chloride or solutions of equivalent effective ion concentrations of other salts. Salt-mediated inhibition was fully reversible by dilution and was independent of substrate concentration. Inhibition was a function of the identity of the salt anion within a Hofmeister (lyotropic) series: I- > SCN- > NO3- > C1- > F-, and, in these terms, was not significantly different for a series of inorganic chlorides (Li+, Na', K+, Cs'). The effects of salts on the natural lipoprotein substrates, chylomicrons, and very low density lipopro- teins were similar to those obtained with a synthetic lipid- protein substrate complex. These findings are discussed in the light of recent ideas on the activation of lipoprotein lipase.