Publisher Summary This chapter describes the assay method, isotopic method, purification procedure, and properties of β -Alanine- α - alanine transaminase of Pseudomonas . Enzymatic activity is best determined colorimetrically by testing for malonic semialdehyde. The measurement for malonic semialdehyde is based on the formation of a red-colored azo compound; this involves the reaction of p -nitroaniline and sodium nitrite to form a diazonium salt, followed by the coupling of the salt to malonic semialdehyde to yield the red azo dye. The isotopic method is based on the measurement of the radioactivity of C 14 -carbon dioxide which was liberated from malonic semialdehyde on decarboxylation with aniline citrate catalyst. The purified enzyme preparation also catalyzes transamination reactions between various other amino acids. From the isotopic studies, it appears that monocarboxylic amino acids containing an amino group at the β -, γ -, and ɛ -positions can serve as an efficient amino donor. Maximum activity of the enzyme is demonstrated at pH 9.2. However, pH 8.0 is used for routine assay, since malonic semialdehyde polymelizes nonenzymatically and also condenses with β -alanine at alkali pH.

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