Enzymatic specifity

The hierarchical order of El, E2 and E3 activity correlates with an increase in enzymatic specificity which ensures selective ubiquitin modification of distinct... 

The enzymatic specificity of diphtheria toxin deserves special comment. The toxin ADP-ribosylates EF-2 in all eukaryotic cells in vitro whether or not they are sensitive to the toxin in vivo, but it does not modify any other protein, including the bacterial counterpart of EF-2. This narrow enzymatic specificity has called attention to an unusual posttranslational derivative of histidine, diphthamide, that occurs in EF-2 at the site of ADP-ribosylation (see fig. 1). Although the unique occurrence of diphthamide in EF-2 explains the specificity of the toxin, it raises questions about the functional significance of this modification in translocation. Interestingly, some mutants of eukaryotic cells selected for toxin resistance lack one of several enzymes necessary for the posttranslational synthesis of diphthamide in EF-2 that is necessary for toxin recognition, but these cells seem perfectly competent in protein synthesis. Thus, the raison d etre of diphthamide, as well as the biological origin of the toxin that modifies it, remains a mystery. 

Interferences. The strategy of enzymatic translation of SO into H2C>2 results in a highly detectable product and the enzymatic specificity of the translation reaction constitute the principal merits of the approach. Therein lies its vulnerability as well interference from H2O2, the translation product, concurrently present in the sample gas. 

The basic question of mimetic catalysis is the determination of physicochemical properties of enzymes to be simulated in the synthesized biomimic in accordance with the reaction modeled. Firstly, let us try to answer one of the key questions that arise in biomimic construction how important is it to reach the enzymatic specificity in the synthesis of their analogs To put it another way, should the dynamic (tertiary) structure of the enzyme responsible for the selectivity control mechanism be simulated by active site protection from competitive admixtures This feature of the enzymes distinguishes them from usual catalysts. 

As an additional example of enzymatic specificity, consider the enzyme DNA polymerase, which synthesizes a polymer of the four basic nucleic acid units (adenosine, guanosine, thymosine, and cytosine) on a template strand of DNA. This enzyme exhibits an extraordinarily high degree of fidelity in the copies it produces typically <1 error per 10 nucleotides polymerized. 

In protease-mediated peptide synthesis, the enzymatic specificity prevents the formation of by-products often formed in the course of conventional chemical synthesis. 

Studies on the structure of DNA are much more dependent on physical and chemical data than on enzymatic. Specific biological functions have been found for DNA from various sources, so it is concluded that specific structures of individual DNA molecules exist, perhaps each structure related to a genetic function. The bases in DNA appear to occur in pairs adenine + thymine and guanine cytosine. The struc-... 

Cell suspension cultures of soya were incubated with mixtures of positional and geometrical isomers of [l- C]octadecenoic acids in order to determine enzymatic specificities for the incorporation of individual isomeric fatty acids into the glycerolipids, for instance triacylglycerols [60]. It is obvious from the data given in Table 3 that A9 isomers of both mixed substrates, (Z)-and f J-octadecenoic acids, are preferentially incorporated into the sn-2 position of the glycerol backbone, whereas a much lower percentage of these acyl moieties are esterified to the... 

Enzym/Ferment enzyme Enzymaktivitat (katal) enzyme activity (katal) Enzymhemmung enzymatic inhibition, repression of enzyme, inhibition of enzyme Enzymreaktion enzymatic reaction Enzymspezifittit enzymatic specificity, enzyme specificity epidermal/... 

Proteins with the same enzymatic specificity but which can be made into different molecular forms by physiochemical techniques. 

Table 1. Enzymatic specificity of amide bond formation...

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