Enzymes chelating characteristic

Recently, Hayashi (92) suggested that the chelating characteristics of LAL could be involved with its toxicity. Since LAL is a strong chelator, LAL could potentially remove metal ions from metaloenzymes, thereby inhibiting the enzyme. Inhibition of carboxypeptidase-B and alcohol dehydrogenase were demonstrated as examples. 

Lanthanide chelates also can be used in FRET applications with other fluorescent probes and labels (Figure 9.51). In this application, the time-resolved (TR) nature of lanthanide luminescent measurements can be combined with the ability to tune the emission characteristics through energy transfer to an organic fluor (Comley, 2006). TR-FRET, as it is called, is a powerful method to develop rapid assays with low background fluorescence and high sensitivity, which can equal the detection capability of enzyme assays (Selvin, 2000). 

Pyrazolate-based dinucleating hgands have proven useful to control crucial characteristics of the dicopper core, such as the Cu - Cu separation and the electronic properties of the metal ions, by variation of the chelate side arms attached to the heterocycle (31). This leads to greatly differing activities in the catalytic oxidation of DTBC mediated by those dicopper complexes [133,135]. While most of the pyrazolate-derived complexes 31 display an enzyme-hke Michaehs-Menten type kinetic behavior, it is apparent that both the Cu - Cu separation as well as the redox potential play an important... 

Since protein complex formation and Ca2+ are critical to cell fixation within a tissue, dissociation media usually contain some type of proteolytic enzyme and the Ca2+ chelator, EDTA. The proteolytic enzyme can be of general specificity, such as trypsin, or can be a more targeted enzyme, such as a collagenase selective for the collagen-type characteristic of the tissue of interest. Hyaluronidase has been also used with matrix rich in hyaluronic acid, such as for isolation of duodenal entero-cytes. In all cases, the appropriate incubation times and concentrations to achieve cell dispersal, but retain high viability, need to be determined empirically. One factor... 

A metal atom is essential to the catalytic activity of carboxypeptidase A (53). The enzyme, as isolated, contains one gram atom of zinc per molecular weight of 34,600. Removal of the metal atom, either by dialysis at low pH or by treatment with chelating agents, gives a totally inactive apoenzyme. Activity can be restored by readdition of zinc or a number of other divalent metal ions (Table VII). The dual activity of carboxypeptidase towards peptides and esters is quite sensitive to the particular activating metal ion. Thus, the cobalt enzyme has twice the activity of the native zinc enzyme toward peptides but the same activity toward esters. Characteristic peptidase and esterase activities are also observed for the and Mn enzymes as well while the Cd ", Rh ", and Pb " en-... 

The use of immobilised cells for industrial and analytical enzymic processes is prophetically advantageous, the problems of isolation of the enzyme(s) and separation of the enzyme(s) from the product being avoided. However, the majority of the reaction currently used for direct enzyme immobilisation would cause cell death if applied to cells. Our approach has been based on the ability of water-insoluble metal hydroxides to chelate and retain peptides, proteins, etc. including enzymes. From various studies it was concluded that gelatinous titanium and zirconium hydroxide matrices are effective matrices for enzyme etc. immobilisation. Their advantages include low cost, convenient preparation (which may be conducted in any location without specialised facilities), the absence of any need for pre-preparation, ability to couple enzyme at neutral pH, the high retentions of specific activity of the enzyme on immobilisation, and the ability of modification to exert microenvironmental effects on and thereby alter the characteristics of the immobilised enzyme. 

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