Cofactor-enzyme affinity complexes

Affinity complexation — Many proteins have affinities for other molecules that can be exploited to alter their retention characteristics in IEC. For example, some enzymes may be combined with synthetic substrates, cofactors, or products.1315 The same principle can be applied to other protein/receptor systems. One well-characterized example is the change in chromatographic behavior of fructose 1,6-diphosphatase in the presence of its negatively charged substrate... 

Enzyme electrodes containing cross-linked cofactors, polypeptides or protein affinity complexes... 

Electrodes functionalized with monolayers of enzyme cofactors (e.g. NAD+-monolayers) demonstrate the ability to form stable affinity complexes with their respective enzymes [301]. These interfacial complexes can be further cross-linked to produce integrated bioelectrocatalytic matrices consisting of the relay-units, the cofactor, and the enzyme molecules. Electrically contacted biocatalytic electrodes of NAD+-dependent enzymes have been... 

The reduction in enzymatic activity that results from the formation of nonproductive enzyme complexes at high substrate concentration. The most straightforward explanation for substrate inhibition is that a second set of lower affinity binding sites exists for a substrate, and occupancy of these sites ties up the enzyme in nonproductive or catalytically inefficient forms. Other explanations include (a) the removal of an essential active site metal ion or other cofactor from the enzyme by high concentrations of substrate, (b) an excess of unchelated substrate (such as ATP" , relative to the metal ion-substrate complex (such as CaATP or MgATP ) which is the true substrate and (c) the binding of a second molecule of substrate at a subsite of the normally occupied substrate binding pocket, such that neither substrate molecule can attain the catalytically active conformation". For multisubstrate enzymes, nonproductive dead-end complexes can also result in substrate inhibition in the presence of one of the reaction... 

Virtually all microorganisms—with the exception of certain lactobacilli— require iron as cofactor of many metabolic enzymes and regulatory proteins because of its ability to exist in two stable oxidation states. Although iron is one of the most abundant elements in the environment, it is often a limiting factor for bacterial growth. This is so because of the formation of insoluble ferric hydroxide complexes under aerobic conditions at neutral pH, which impose severe restrictions on the availability of the element. Consequently, bacteria have evolved specialized high-affinity transport systems in order to acquire sufficient amounts of this essential element. 

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