Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Penicillin amidase, alpha-chymotrypsin and urease have been immobilized in water-soluble nonstoichiometric polyelectrolyte complexes (N-PEC). N-PEC are formed by modified poly(N-ethyl-4-vinyl-pyridinium bromide) (polycation) and excess poly(methylacrylic acid) (polyanion). N-PEC are a new class of polymers capable, characteristically, of phase transitions solution in equilibrium precipitate induced by slight change in pH or ionic strength. Neither the chemical structure of the carrier nor the number of cross-linkages between an enzyme and a carrier change on phase transition. That gives an unique opportunity to elucidate the difference between enzymes immobilized on water-soluble and water-insoluble supports. A detailed study of the phase transition effect on thermal stability of the enzymes and protein-protein interactions has been carried out. The following effects were found. Pronounced thermal stabilization of penicillin amidase and urease may be achieved on two conditions: the enzyme is in the precipitate; (b) the enzyme is linked to the N-PEC nucleus. Then the thermal stability of N-PEC-bound penicillin amidase increases 7-fold at pH 5.7, 60 degrees C, and 300-fold at pH 3.1, 25 degrees C, compared to the native enzyme. For urease, the thermal stabilization increases 20-fold at pH 5.0, 70 degrees C. The localization of enzyme on N-PEC has been established by titration of alpha-chymotrypsin bound to a polycation or polyanion with basic pancreatic trypsin inhibitor. Both in solution (pH 6.1) and in N-PEC precipitate (pH 5.7), an alpha-chymotrypsin molecule bound to a polyanion is fully exposed to the solution. If the enzyme is bound to a polycation, only 20% of alpha-chymotrypsin molecules in the precipitate and 40% in solution retain their ability for protein-protein interactions. This means that a polycation-bound enzyme is localized in the hydrophobic nucleus of the complex, whereas the polyanion-bound enzyme sits on the hydrophilic shell of the complex. On pH-induced phase transition (pH decreases from 6.1 to 5.7), there occurs a stepwise decrease in penicillin amidase activity which is due to a 9.8-fold increase in the Km for 2-nitro-4-phenylacetamidobenzoic acid. Change of the catalytic activity and thermal stability of N-PEC-bound penicillin amidase is fully reversible and reproducible. Such soluble-insoluble immobilized enzymes with controllable thermal stability and activity may be used for simulating events in vivo and in biotechnology.
 ...
PMID:Enzymes in polyelectrolyte complexes. The effect of phase transition on thermal stability. 397 68

A mathematical model has been developed for the internal pH control in immobilized enzyme particles. This model describes the kinetics of a coupled system of two enzymes, immobilized in particles of either planar, cylindrical, or spherical shape. The enzyme kinetics are assumed to be of a mixed type, including Michaelis-Menten kinetics, uncompetitive substrate inhibition, and competitive and noncompetitive product inhibition. In a case study we have considered the enzyme combination urease and penicillin acylase, whose kinetics are coupled through the pH dependence of the kinetic parameters. The hydrolysis of urea by urease yields ammonia and carbon dioxide, whereas benzylpenicillin (Pen-G) is converted to 6-amino penicillanic acid and phenyl acetic acid by penicillin acylase. The production of acids by the latter enzyme will cause a decrease in pH. Because of the presence of the ammonia-carbon dioxide system, however, the pH may be kept under control. In order to obtain information about the optimum performance of this enzymatic pH controller, we have computed the effectiveness factor and the conversion in a CSTR at different enzyme loadings. The results of the computer simulations indicate that a high conversion of Pen-G may be achieved (80-90%) at bulk pH values of about 7.5-8.
 ...
PMID:Mathematical model for internal pH control in immobilized enzyme particles. 1855 76