Nicotinamide-Adenine Dinucleotide Phosphate-Dependent Isocitrate Dehydrogenase(IDPc)is an important enzyme essential for survival of all organisms.Many studies have been conducted to isolate IDPc and explore its kinetic parameters in mammals,plants and microorganisms.However,in fish,the related information is very scarce.The aim of the study is to purify and characterize IDPc from yellow catfish hepatic cytoplasm,which will provide some crucial information on the catalytic and regulatory mechanism of the enzyme in liver of yellow catfish.The purification processes include permeation chromatography on Sephadex G-100 gel,chromatographic adsorption by DEAE Sepharose,permeation chromatography on Sephadex G-25 gel and finally chromatographic adsorption by DEAE Sepharose again.The specific IDPc activity is 7.94 U/mg,and its molecular weight after SDS polyacrylamide slab gel electrophoresis is 36.7 ku.The optimum pH,and temperature for the enzyme are 8.0 and 65℃ respectively.Using Arrhenius plots,the enzyme has the activation energy of 81.33 kJ/mol.The Km values of the substrates NADP⁺ and IC are 0.056 mmol/L and 0.175 mmol/L,respectively.The Vmax values of IDPc with NADP⁺ and IC as the substrates are 9.04 U/mg and 10.51 U/mg,respectively.The enzyme of IDPc is inhibited by NADPH in a competitive manner with the K_i value of 0.034 mmol/L.The activity of IDPc is greatly dependent on the binding of divalent metal ions with the active order of Mn²⁺>Mg²⁺>Zn²⁺>Ca²⁺>Cu²⁺.Ca²⁺ and Zn²⁺ are both the activator and inhibitor of IDPc,however,Cu²⁺ showed no effects on the enzyme.The comprehensive information of enzymatic properties may help to better understand the mechanism of catalysis and regulation of IDPc in fish.