Improvement of catalytic properties of the strain producing aspartase Pectobacterium carotovorum in the process of obtaining L-aspartic acid

The paper presents the results of studies to determine the optimal functioning parameters of aspartase and fumarase of the bacterial strain P. carotovorum MDC-8727, an aspartase producer. The temperature and pH optima of both enzymes are close and are in the range of T (35-40 °C) and pH (8.5-9.0). At a temperature of 50 °C, the thermal stability of aspartase is twice higher than that of fumarase. It was found that thermal treatment of cell biomass in the culture broth at low pH values contributed to the partial inactivation of fumarase. A similar treatment of cells at temperature of 50 °C and pH 5 for 90 minutes contributed to the complete inactivation of fumarase without harming the aspartase activity. fumarase, aspartase, L-aspartic acid, biotransformation

A Novel Mechanism for Resistance to the Antimetabolite N -Phosphonoacetyl-l-Aspartate by Helicobacter pylori

ABSTRACT The mechanism of resistance toN-phosphonoacetyl-l-aspartate (PALA), a potent inhibitor of aspartate carbamoyltransferase (which catalyzes the first committed step of de novo pyrimidine biosynthesis), inHelicobacter pylori was investigated. At a 1 mM concentration, PALA had no effects on the growth and viability ofH. pylori. The inhibitor was taken up by H. pylori cells and the transport was saturable, with aKm of 14.8 mM and aV max of 19.1 nmol min−1 μl of cell water−1. By 31P nuclear magnetic resonance (NMR) spectroscopy, both PALA and phosphonoacetate were shown to have been metabolized in all isolates of H. pyloristudied. A main metabolic end product was identified as inorganic phosphate, suggesting the presence of an enzyme activity which cleaved the carbon-phosphorus (C-P) bonds. The kinetics of phosphonate group cleavage was saturable, and there was no evidence for substrate inhibition at higher concentrations of either compound. C-P bond cleavage activity was temperature dependent, and the activity was lost in the presence of the metal chelator EDTA. Other cleavages of PALA were observed by 1H NMR spectroscopy, with succinate and malate released as main products. These metabolic products were also formed when N-acetyl-l-aspartate was incubated with H. pylori lysates, suggesting the action of an aspartase. Studies of the cellular location of these enzymes revealed that the C-P bond cleavage activity was localized in the soluble fraction and that the aspartase activity appeared in the membrane-associated fraction. The results suggested that the twoH. pylori enzymes transformed the inhibitor into noncytotoxic products, thus providing the bacterium with a mechanism of resistance to PALA toxicity which appears to be unique.