Amino-acid Composition and Partial Specific Volume of Citrate Oxaloacetate Lyase

Abstract

STUDIES of the amino-acid composition of citrate oxaloacetate lyase (citrate lyase) from Aerobacter aerogenes were made using the pure enzyme prepared by methods previously described^1,2. The amino-acid composition of the enzyme was determined using the technique of high-voltage electrophoresis to separate the amino-acids in a protein hydrolysate³. Hydrolysates of two quantities of enzyme (5.0 mg), by ‘AnalaR’ hydrochloric acid (6 N) in sealed tubes at 110° for 24 h and 72 h, respectively, were prepared. The protein in the solution to be hydrolysed was estimated by the method of Hoch and Vallee⁴. The method of amino-acid separation and analysis was similar to that used by Atfield and Morris⁵, using a cadmium ninhydrin reagent. The apparatus was based on the general design of Gross⁶, with longer coiling plates, as favoured by Atfield and Morris⁵. The concentration of each amino-acid, after elution from the strip, was read from concentration-absorbancy graphs previously constructed using similarly treated standard solutions of amino-acids. Absorbancies were read on a Unicam SP 600 spectrophotometer at 505 mµ. The relative colour values of the cadmium ninhydrin complexes with individual amino-acids on a molar basis are given in Table 1; they show wide variations (cf. Helimann et al.⁷). Proline was estimated in the hydrolysate, and hydroxyproline shown to be absent, by estimation with cadmium isatin reagent.