Abstract
Aspartase from Lactobacillus murinus CNRZ 313 (L-aspartate ammonia lyase, E.C. 4.3.1.1.), is one of the enzymes of aspartate metabolism in lactic acid bacteria. The growth of this microorganism in LAPTg medium is not altered by the addition of L-aspartate. Aspartase is a thermolabile enzyme. Its activity was not changed in one month at temperatures lower than 0°C, independently of the presence of 10% glycerol or 0.05M MgCl2. Maximum activity occurred at 32°C and pH 7.5 in 0.15M Tris-HCl pH 7.5. At pH values different from the optimum, positive cooperation between substrate molecules was observed.
The Km values for L-aspartate at pH 7.5 and 7.0 were: 3.7×10-2M and 9.0×10-2M respectively. The pK values of pKa 6.75 and pKb 7.35 were calculated from Dixon plots. The ΔG of the reaction was calculated by Arrhenius plot. The values were 4, 807cal mol-1 below 25°C and 2, 665cal mol-1 above 25°C. Both 10-3M HgCl2 and NaCN had inhibitory effects.
