Chung C D, Bieber L L
Department of Biochemistry, Michigan State University, East Lansing 48824.
J Biol Chem. 1993 Feb 25;268(6):4519-24.
Carnitine octanoyltransferase (COT) purified from rat liver microsomes has K0.5 values between 1.0 and 4.0 microM for saturated 6-carbon to 16-carbon length acyl-CoAs, with little differences in Vmax values. The reaction rate is linear with time in the forward direction (acyl-CoA-->acylcarnitine), but it increases with time when assayed in the reverse direction (acylcarnitine-->acyl-CoA). The K0.5 for decanoylcarnitine and CoASH are 0.3 mM for CoASH and between 1.0 and 4.0 mM for decanoylcarnitine. The kinetic data indicate that the enzyme functions in the direction of acyl-carnitine formation. It is moderately inhibited by aminocarnitine, and D-carnitine and etomoxiryl-CoA are weak inhibitors; malonyl-CoA does not inhibit the enzyme. The enzyme has little, if any, capacity to use valproylcarnitine, 3-methylglutarylcarnitine, or pivaloylcarnitine as a substrate. Polyclonal antibodies prepared against COT give a positive Western blot against the purified enzyme and against a protein in microsomes having the molecular mass of COT (53 kDA). Antimitochondrial CPT and antiperoxisomal CAT did not show appreciable cross-reactivity with purified microsomal COT. The inhibitor data, the kinetic data, the molecular masses, and the Western blotting profiles all show that the enzyme purified from rat liver microsomes is a different carnitine acyltransferase than those previously purified from other organelles.
从大鼠肝脏微粒体中纯化得到的肉碱辛酰基转移酶（COT），对于饱和的6碳至16碳长度的酰基辅酶A，其K0.5值在1.0至4.0微摩尔之间，Vmax值差异不大。在正向反应（酰基辅酶A→酰基肉碱）中，反应速率与时间呈线性关系，但在反向反应（酰基肉碱→酰基辅酶A）中测定时，反应速率随时间增加。癸酰肉碱和辅酶A的K0.5值，辅酶A为0.3毫摩尔，癸酰肉碱为1.0至4.0毫摩尔。动力学数据表明该酶在酰基肉碱形成方向上起作用。它受到氨基肉碱的中度抑制，D-肉碱和依托莫昔利辅酶A是弱抑制剂；丙二酰辅酶A不抑制该酶。该酶几乎没有能力将丙戊酰肉碱、3-甲基戊二酰肉碱或新戊酰肉碱用作底物。针对COT制备的多克隆抗体，对纯化的酶以及对微粒体中分子量为COT（53 kDa）的一种蛋白质进行蛋白质免疫印迹检测呈阳性。抗线粒体肉碱棕榈酰转移酶（CPT）和抗过氧化物酶体肉碱乙酰转移酶（CAT）与纯化的微粒体COT没有明显的交叉反应。抑制剂数据、动力学数据、分子量以及蛋白质免疫印迹图谱均表明，从大鼠肝脏微粒体中纯化得到的这种酶是一种与先前从其他细胞器中纯化得到的不同的肉碱酰基转移酶。
