Ivan K. Smith

Cystine lyase from cabbage

Publisher Summary This chapter discusses the determination cystine lyase from cabbage. Cystine lyase has been isolated from the roots and leaves of several members of the Cruciferae belonging to the genera Brassica. The trivial name of the enzyme is probably a misnomer, in the sense that it implies a specificity and physiological function. Although quantitation of cysteine persulfide is not difficult, most investigators prefer to assay enzyme activity by measuring the initial rate of pyruvate formation. This is done either by following the oxidation of NADH in the presence of lactate dehydrogenase, or by preparing the dinitrophenylhydrazone, treating with base to develop color, and measuring absorbance at 520 nm. In the course of purification, Commercially available head cabbage (Brassica oleracea vat. capitata) leaves (1 kg) are deveined, washed, and homogenized in 1 liter of ice-cold 0.1 M sodium phosphate at pH 7.2, containing 0.5 m M pyridoxal phosphate, in a Waring Blendor at top speed for 3 min. The debris is removed by straining through cheesecloth, and the filtrate is centrifuged at 10,000 g for 20 min.