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Glutamicacid decarboxylase （GAD） is the key enzyme for catalyzingα-carboxyl to decarboxylase of L-MSG. It is widely distributed, it exists in plants,animals and microgranisms of nature. GAD is more likely as special diagnostic enzyme for forecasting and distinguishing IDDM, so it is very significative for understanding its structure and character. GABA, which is the production catalyzed by GAD has effect of regulating blood pressure, promoting nerve stability and promoting brain blood circulation, so people are devoting themselves to develop food that is GABA enrichment.This text has researched GAD, which is preserved by fermentation engineering laboratory of Heilongjiang university. It has also optimized the culture medium and the condition of cultivate of GAD, the separation and purification by cell discruption, （NH4）2SO4 and salt precipitation, Sepharose Fast Flow ion-exchange column and Sephadex G-100. Then, it has used colorimetry to measure the activity of GAD, in the meantime, it also has used SDS-PAGE to measure the punity of GAD. Purification fold of GAD is 32.5, specific activity of GAD is 81.25U/mg and recovery is 15.1%. At last tis text has introduced the main properties of GAD.The optimum fermentation medium of GAD, is The addition amount of L-MSG is 5g/L, glucose 10g/L, yeast powder 17.5g/L, peptone 5g/L, anhydr-sodiumacetate 2g/L, MgSO4·7H2O 0.58g/L,MnSO4·4H2O 0.25g/L,NaCl 0.01g/L,FeSO4·7 H2O 0.001g/L,initial pH is 6.5 and the disitilled water is volumed to 1 000mL.The optimum fermentation condition of GAD, is the inoculum amount was 4%, culture temperature was 37℃, culture time was 16h.The molecular weight of GAD, which is obtained by SDS-PAGE is 70k.The main properties of GAD as follows , when the concentration of L-MSG is 100mmol/L, GAD has highest activity, the concentration of GAD is 3.16%,the optimal temperature is about 37℃, the optimal pH is 5, when the addition amount of PLP is 0.1mol/L, GAD has highest activity. The Michaelis constant of GAD is Km=0.3658mmol/L, Vmax=3.03μmol/L.
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