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At least 523 records · Page 29Linked to original sources
PubMed1999

pH gradients in immobilized amidases and their influence on rates and yields of beta-lactam hydrolysis.

The pH gradients developing within immobilized biocatalysts during hydrolysis of penicillin G and glutaryl-7-aminocephalosporanic acid have been estimated both theoretically and experimentally. For the latter a fluorimetric method for the direct measurement of the average pH value within the carrier during reaction has been developed using the pH-dependent fluorescence intensity of an enzyme-bound fluorophore determined with a fiber bundle. The theoretical calculations were based on a model for the hydrolysis with immobilized enzymes using a kinetic expression with five pH-dependent, measurable kinetic and equilibrium constants. The transport reaction differential equation which considers the laminar boundary layer has been solved numerically for the key component. The calculated values agreed well with the experimental data. Under the typical reaction conditions of penicillin G hydrolysis the average pH value in the carrier was 1 and 2.5 pH units below the bulk pH (=8) with and without buffer, respectively. The corresponding changes for the hydrolysis of glutaryl-7-aminocephalosporanic acid at bulk pH 8 in the presence of buffer was 0.5. This demonstrates the existence of considerable pH gradients in carriers during hydrolytic reactions, even in buffered systems with negligible mass transfer resistance. The low pH value causes suboptimal reaction rates, reduced equilibrium conversion, and reduced enzyme stability. These pH gradients can be minimised by using buffers with pK values approximately equal to the bulk pH used for the hydrolysis. The prediction quality of the model has been tested applying it to fixed bed reactor design. The reduction in rate and yield due to concentration and pH gradients can be overcome with simple measures such as high initial pH value and pH adjustments in segmented or recycling fixed bed reactors. Thus, enzymatic conversions with high yield and high operational effectiveness are achieved.

Amidohydrolases↗
PubMed1999

[Human drug metabolizing enzymes III. Epoxide hydrolases, esterases, and amidases].

In this review we focus on human hydrolytic enzymes that participate in the metabolism of xenobiotics. Although hydrolysis in most of the cases result in detoxication, in some cases hydrolysis may lead to activated molecules that may attack macromolecules (proteins, RNAs, DNAs), resulting in toxicity. We have summarised the data available on these enzymes concerning their catalytic profile and specificity, inhibition, induction properties, their possible role in the generation of toxic compounds, their importance in clinical practice and drug development.

Amidohydrolases↗
PubMedDate not supplied

[Activity and properties of L-lysine amidase in Salmonella strains].

Distribution, activity level and properties of alpha-lysinamidase have been studied in Salmonella strains. The Km value for L-lysinamide was calculated to be 4.2 mM and for L-alpha-aminocaprolactame--5.1 mM. This enzyme, parallel with lysinamide, catalyzes hydrolysis of alpha-aminocaprolactam and leucinamide. Asparagine, glutamine, caprolactam, triptophanamide were not lysinamidase substrates.

Amidohydrolases↗