Amino acid sequences specific product

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

The O-ECAT reagent is a superior alternative to the use of 2,4-dinitrophenylhydrazine (DNPH Chapter 1, Section 1.1) in the study of protein oxidation. DNPH modification produces detectable complexes, but it does not provide information as to what amino acids are involved. O-ECAT modifies carbonyl end products of protein oxidation and in addition, it can provide exact information as to the amino acids that were oxidized. Mass spec analysis of modified proteins performed after proteolysis gives the exact amino acid sequences including the sites of O-ECAT reagent modification. The same antibody that is specific for the metal chelate portion of the standard ECAT reagent also can be used to capture and detect the O-ECAT... 

He, X.Z. and Dixon, R.A., Affinity chromatography, substrate/product specificity, and amino acid sequence analysis of an isofiavone 0-methyltransferase from alfalfa (Medicago sativa L.). Arch. Biochem. Biophys., 336, 121, 1996. 

OSCs that have been functionally characterised by expression in yeast are hsted in Table 2, and the relatedness between the amino acid sequences of these enzymes is illustrated in Fig. 3. The conserved features of this OSC superfamily and the differences between them that may confer product specificity are considered below. 

In vitro determination of specific antigens in products using classical physicochemical and biochemical methods, which rely on the determination of amino acid sequences in proteins and their tertiary structure (see Section 3.4) as well as immunodetection methods using commercially available analytical tests... 

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