Effects of Some Complexing Agents and Modified Bovine Serum Albumins on Lecithin-Cholesterol Acyltransferase Inhibition caused by Cu²⁺ or Hg²⁺ Ions

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Lecithin-cholesterol acyltransferase [EC 2. 3. 1. 43] (LCAT) activity in human plasma was inhibited by the addition of 1×10^-3M Cu²⁺ or Hg²⁺ ions as well as Zn²⁺ or Cd²⁺ ions. In contrast, the acyltransferase activity was stimulated by the addition of 1×10^-3 M cysteine, mercaptoethanol, dimercaptosuccinate, penicillamine, thioglucose or thiourea but not by the addition of 1×10^-3 M histidine or ethylenediaminetetraacetic acid (EDTA). The most effective stimulation was obtained by the addition of mercaptoethanol. On the other hand, dimercaptoethanol among the sulfhydryl agents mentioned above effectively reversed the acyltransferase inhibition caused by Zn²⁺ or Cd²⁺ ions but not that caused by Cu²⁺ or Hg²⁺ ions. EDTA completely reversed the acyltransferase inhibition caused by Cu²⁺ or Cd²⁺ ions but not that caused by Hg²⁺ ions. Histidine slightly reversed the acyltransferase inhibition caused by Cu²⁺, Cd²⁺ or Zn²⁺ ions. Furthermore, native, acetylated or succinylated albumin effectively reversed the acyltransferase inhibition caused by Zn²⁺ or Cd²⁺ ions but not that caused by Cu²⁺ or Hg²⁺ ions.