Enzyme specific catalytic activity

The metabolic control is exercised on certain key regulatory enzymes of a pathway called allosteric enzymes. These are enzymes whose catalytic activity is modulated through non-covalent binding of a specific metabolite at a site on the protein other than the catalytic site. Such enzymes may be allosterically inhibited by ATP or allosterically activated by ATP (some by ADP and/or AMP). 

They have an exceedingly high specific activity per active site the turnover number y is as high as 10 to 10 s in certain enzyme reactions, while at ordinary electrocatalysts having a number of reaction sites on the order of 10 cm , yhas a value of about 1 s at a current density of lOmA/cm. Thus, the specific catalytic activity of tfie active sites of enzymes is many orders of magnitude fiigher tfian tfiat of all other known catalysts for electrochemical (and also chemical) processes. 

Receptor-effector mechanisms include (1) enzymes with catalytic activities, (2) ion channels that gate the transmembrane flux of ions (ionotropic receptors), (3) G protein-coupled receptors that activate intracellular messengers (metabotropic receptors), and (4) cytosolic receptors that regulate gene transcription. Cytosolic receptors are a specific mechanism of many steroid and thyroid hormones. The ionotropic and metabotropic receptors are discussed in relevance to specific neurotransmitters in chapter 2. 

The level of enzyme needed can influence the choice of preparation used for the study. Microsomal preparations from cell cultures allow the use of higher concentrations of active enzyme per unit volume than use of whole cells or cell lysates. The use of whole, viable cells allows the use of longer incubation times but at a lower enzyme concentration per unit volume. In addition, adequate oxygen transfer and nutrient concentrations are needed to maintain culture viability. These requirements impose limitations on cell concentration. In addition, microsomes cannot be efficiently prepared from all cultured cell types. We have found that standard microsome preparation procedures as used for human or rodent liver were unsuitable for isolating active enzymes from human lymphoblasts, and this appears to be a general property of cultured cell lines. Specific catalytic activities in microsomes were lower than for whole cell lysates. This loss of activity appears to happen in other mammalian cell systems which has led to the common use of whole cell lysates.With human lymphoblasts, shortening the length of... 

By using specific catalytic activities, the differences in V ax due to any factor are automatically compensated for in the calculation. Because this method establishes relative contribution, there is no a priori need to use the same units for both components of the RAF calculation as long as the same units are used within the cDNA-expressed enzyme data set and the human tissue data set. Moreover, knowledge of the P450 content in either the cDNA expression system or in human liver microsomes is not necessary in order to make an interpretation. 

Enzymes are chiral molecules with specific catalytic activities. For example, when an acylated amino acid is treated with an enzyme like hog kidney acylase or car-boxypeptidase, the enzyme cleaves the acyl group from just the molecules having the natural (l) configuration. The enzyme does not recognize D-amino acids, so they are unaffected. The resulting mixture of acylated D-amino acid and deacylated L-amino acid is easily separated. Figure 24-5 shows how this selective enzymatic deacylation is accomplished. 

Proteins constitute the largest portion of living matter in all types of cells. They serve as structural elements in cells and tissues, show specific catalytic activity, function as enzymes, and are found in cell membranes. Most IR and classical Raman studies focus on the characterization of protein secondary structures by using sets of absorption bands and diffusion Raman lines reflecting especially the motions of peptide groups (Sec. 

Enzymes are catalytically active proteins that are involved in every in vivo transformation. They enhance the rates of biochemical reactions by 10 to 10 2 by reduction of the free energy of activation. Two distinctive properties of enzymes are their high substrate specificity and the narrow range of conditions under which they are effective. They usually catalyze one reaction of a few substrates. Activities are dependent on pH, temperature, the presence of cofactors, as well as concentrations of substrates and products. Enzymes perform specific reactions because they possess cavities in which substrates are oriented white they are transformed (Figure 1). This process involves interaction of the substrate with amino acids of the enzyme. 

For the production of an effective monoclonal antibody it is crucial to raise it from a well-designed transition state analogue. Besides not resembling the product too much in order to avoid product inhibition, this hapten should mimic the transition state as closely as possible to maximize its stabilization by the antibody generated. Utilizing the extraordinary specificity of the immune system by this means, the combining site of the antibody is programmed to exhibit a specific catalytic activity. This technique has been directed toward the development of selective reactions which are chemically difficult to achieve, for example disfavored , and for which no suitable enzyme is available. 

Regulation of ribonucleotide reductase is complex. The binding of dATP (deoxyadenosine triphosphate) to a regulatory site on the enzyme decreases catalytic activity. The binding of deoxyribonucleoside triphosphates to several other enzyme sites alters substrate specificity so that there are differential increases in the concentrations of each of the deoxyribonucleotides. This latter process balances the production of the 2 -deoxyribonucleotides required for cellular processes, especially that of DNA synthesis. 

Poly(ADP-ribose) polymerase (95% homogeneous) and coenzymic DNA were isolated from calf thymus [1]. Its specific catalytic activity was 1066 nmol ADP-ribose incorporated per mg protein in 1 min. Details of isolation, DNA-cellulose binding as well as labeling of the enzyme with I, a procedure that does not alter catalytic activity, are... 

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