Lecithin-cholesterol acyltransferase [EC 2. 3. 1. 43] (LCAT) activity in human plasma was inhibited by the addition of 1×10
-3M Cu
2+ or Hg
2+ ions as well as Zn
2+ or Cd
2+ 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 Zn
2+ or Cd
2+ ions but not that caused by Cu
2+ or Hg
2+ ions. EDTA completely reversed the acyltransferase inhibition caused by Cu
2+ or Cd
2+ ions but not that caused by Hg
2+ ions. Histidine slightly reversed the acyltransferase inhibition caused by Cu
2+, Cd
2+ or Zn
2+ ions. Furthermore, native, acetylated or succinylated albumin effectively reversed the acyltransferase inhibition caused by Zn
2+ or Cd
2+ ions but not that caused by Cu
2+ or Hg
2+ ions.
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