Purification and Characterization of Cytosolic Glyceraldehyde-3-phosphate Dehydrogenase from the Dromedary Camel

摘要

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (EC 1.2.1.12), a key enzyme of carbon metabolism, was purified and characterized to homogeneity from skeletal muscle of Camelus dromedarius. The protein was purified approximately 26.8 folds by conventional ammonium sulphate fractionation followed by Blue Sepharose CL-6B chromatography, and its physical and kinetic properties were investigated. The native protein is a homotetramer with an apparent molecular weight of approximately 146 kDa. Isoelectric focusing analysis showed the presence of only one GAPDH isoform with an isoelectric point of 7.2. The optimum pH of the purified enzyme was 7.8. Studies on the effect of temperature on enzyme activity revealed an optimal value of approximately 28-32 ℃ with activation energy of 4.9 kcal/mol. The apparent K_m values for NAD~+ and DL-glyceraldehyde-3-phophate were estimated to be 0.025±0.040 mM and 0.21±0.08 mM, respectively. The V_(max) of the purified protein was estimated to be 52.7±5.9 U/mg. These kinetic parameter values were different from those described previously, reflecting protein differences between species.