สำนักราชบัณฑิตยสภา

209 สมศั กดิ์ ด� ำรงค์เลิ ศ และคณะ วารสารราชบัณฑิตยสถาน ปีที่ ๓๗ ฉบับที่ ๑ ม.ค.-มี.ค. ๒๕๕๕ by cytosolic flavin-dependent reductases (flavin reductases) were responsible for unspecific reduction of azo dyes (22, 45, 46). Because quinone reductases and flavin reductase are hypothesized involving the unspecific reduction of azo dyes by bacteria, there- fore, in this study we attempted to determine the activity of these enzymes present in membrane and cytoplasmic fractions of strain A5. For strain A5, it has shown that the high level of NADH: quinone oxidoreductase activity was found in membrane fraction meanwhile the high level of NAD(P)H:flavin oxidoreductase activity was found in cytosolic fraction of the cells (Table 3). TABLE 3  Specific activities of quinone reductase and flavin reductase in membrane-bound and cell extract of Paenibacillus sp. strain A5. Specific activity (μmol min-1 g of protein -1 ) a Enzyme Membrane Cell extract Quinone reductase 81.8 8.8 Flavin reductase 6.8 72.1 a The enzyme activities were determined spectrophotometrically as described in Materials and Methods. Mechanism which AQDS enhance sulfonated azo dyes reduction The proposed mechanism by which AQDS enhance reduction of azo com- pounds encloses two independent reactions: first, the quinones are enzymatically reduced to the corresponding hydroquinones, and second, the hydroquinones cleave the azo dyes in a purely chemical reaction (31, 42, 50). Therefore, both reactions were analyzed separately (Fig. 4). For the first reaction, the experimental results shown that the anaerobic Paenibacillus sp. strain A5 suspensions could drive a large fraction of AQDS to the reduced state (anthrahydroquinone-2,6-disulfonate, AH 2 QDS) as evidenced by the orange color formation and increased absorbance at 450 nm (10)) of the culture medium with