สำนักราชบัณฑิตยสภา

201 สมศั กดิ์ ด� ำรงค์เลิ ศ และคณะ วารสารราชบัณฑิตยสถาน ปีที่ ๓๗ ฉบับที่ ๑ ม.ค.-มี.ค. ๒๕๕๕ the reduction rate of NADH was measured at 348 nm (molar extinction coefficient = 5.9 mM -1 cm -1 ), where reduced and oxidized forms of menaquinone have identical absorbtivity. (ii) NAD(P)H:flavin oxidoreductase The NAD(P)H:flavin oxidoreductase was determined by a modification of the method given by Izumi and Ohshiro (25) and Russ et al (46). The reaction mixture (final volume, 1 ml) for the measurement of the enzyme activity contained 50 mM of Tris-HCl (pH 7.5), 0.5-1 mg protein of cell extract or soluble cell membrane, and 3 µM of riboflavin. The reaction was started by the addition of 250 µM of NADH. The decrease in the concentration of NADH was determined spectrophotometrically at 340 nm, and reaction rates were calculated by using a molar extinction coefficient of 6.2 mM -1 cm -1 . Determination of protein content The protein content of cell extracts and soluble cell membrane were determined by the method of Bradford (6) with bovine serum albumin (Sigma, Fraction V) as the standard. Proteins in whole cells were assayed after adding NaOH to the cells to 1 N concentration, then boiling the cultures for 5 min. The supernatant fractions obtained by centrifuging the suspensions were assayed by the Bradford method, using 1 N NaOH as diluent for the standards. Reduction of AQDS by whole cells of strain A5 and subsequent chemical re- duction of sulfonated azo dyes by reduced AQDS Strain A5 was aerobically grown in MMG until reach the late-exponential growth phase. The cells were harvested by centrifugation, washed and resuspended in Na-K phosphate buffer (50 mM, pH 7.5). One millilitre of the cell suspension (protein content = 0.1 g l -1 ) was transferred to screw cap-glass tube (10 ml.) containing 9 ml of 50 mM Na-K phosphate buffer (pH 7.5) plus glucose (5 mM). The anaerobic incubation was