Apolipoprotein C-III can specifically bind to hepatic plasma membranes

作者：Fang D; Liu B^*

来源：Molecular and Cellular Biochemistry, 2000, 207(1-2): 57-64.

DOI：10.1023/A:1007038129481

• apolipoprotein C-III
• hepatic plasma membranes
• specific binding
• human
• mouse

Apo C-III plays an important role in the metabolism of plasma triglyceride, which can delay the catabolism of triglyceride-rich lipoproteins by interfering with apo E-mediated receptor clearance of remnant particles from plasma. The mechanism of the interference has not yet been defined. To further explore the role of apo C-III, we first injected mice with I-125-apo C-III. The measurement of radioactivity showed that liver took up 3.3-10 fold as much radioactivity as other organs such as heart, spleen, lung, kidney, stomach, large intestine, small intestine, and muscle. This was confirmed by incubating the tissue homogenates of the organs with I-125-apo C-III that the radiolabeled apo C-III specifically bound to only hepatic homogenate. To investigate which subcellular part or parts of hepatic cells play the role of binding to apo C-III, hepatic cell components of nucleus, mitochondria, microsomes and plasma membranes were then incubated with I-125-apo C-III. The radiolabeled apo C-III could specifically bind to only hepatic plasma membranes. Finally hepatic plasma membranes were purified to study the characteristics of the specific binding with apo C-III. Addition of increasing concentration of I-125-apo C-III to human hepatic plasma membranes revealed saturable binding to membranes with a Kd of 0.31 +/- 0.07 mu mol/l. The maximum specific binding capacity was 1.74 +/- 0.45 mu apo C-III/mg membrane protein. In competition studies using unlabeled apo C-III and isolated lipoproteins HDL, LDL and VLDL, only apo C-III and VLDL effectively competed with I-125-apo C-III for membrane binding. The binding of I-125-apo C-III to human liver plasma membranes was Ca2+-independent, and was abolished when plasma membranes were treated with trypsin. The characteristics of I-125-apo C-III binding to mouse liver plasma membranes were similar to those of human liver plasma membranes with the exception of a binding maximum of 1.52 +/- 0.39 mu apo C-III/mg membrane protein. We conclude that apo C-III exhibits high-affinity binding to hepatic plasma membranes, which is saturable, reverse and specific.

• 出版日期2000-4
• 单位中国医科大学