. Biological structure and function; proceedings. Biochemistry; Cytology. SOLUBILIZATION AND PROPERTIES OF THE DPNH DEHYDROGENASE 115 Before leaving the subject it may be worth mentioning that the absolute position and the height of the peak in the near visible region are strongly dependent on pH (Fig. 14). The partly purified enzyme (specific activity = 130) was found to be relatively insensitive to inhibition by /)-chloromercuribenzoate, completely insensitive to dicoumarol (Fig. 3); it did not catalyze the reduction of coenzyme Q^, significantly (with or without added mitochondrial lipid an
. Biological structure and function; proceedings. Biochemistry; Cytology. SOLUBILIZATION AND PROPERTIES OF THE DPNH DEHYDROGENASE 115 Before leaving the subject it may be worth mentioning that the absolute position and the height of the peak in the near visible region are strongly dependent on pH (Fig. 14). The partly purified enzyme (specific activity = 130) was found to be relatively insensitive to inhibition by /)-chloromercuribenzoate, completely insensitive to dicoumarol (Fig. 3); it did not catalyze the reduction of coenzyme Q^, significantly (with or without added mitochondrial lipid and Triton X-ioo), and, under the assay conditions recommended by Wosilait [22], the rate of reduction of menadione at V^^^ was less than 1% of the rate of reduction of ferricyanide. These observations clearly dis- Lipoyl dehydrogenase assay. 04 0'8 1-2 I///1. Iipoamide Fig. 15. Lipoyl dehydrogenase assay of DPXH dehydrogenase. Conditions were as recommended by Massey [6]. The abscissa denotes the reciprocal volumes (in jA.) of 0-058 M Iipoamide present in i ml. reaction mixture. tinguish the enzyme from DT diaphorase [23, 24] and from menadione reductase [22]. Under the conditions of the lipoyl dehydrogenase assay employed by Massey [6] the soluble extract obtained on treatment of FTP with phos- pholipase A shows only a trace of activity on Iipoamide (Fig. 15): ratio of activities on ferricyanide and Iipoamide, respectively, differ bv a factor of about 500 between this preparation and diaphorase (Table II). This trace of lipoyl dehydrogenase activity may well be due to a slight contamination with diaphorase which would be probably removed in the purification pro- cedure. The dehydrogenase may be readily distinguished from DPNH cytochrome c reductase [2] by its much greater stability and bv the extremely low rate of cytochrome c reduction even when assayed under optimal conditions for Mahler's enzyme (Table III). That the residual. Please note that these images are extracted from
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