0-10.0 with an optimum activity at pH 8.0 (Additional file 1: Figure S4a, S4c). Further, the purified enzyme retained 65% activity after 20 min at

60°C, 18% activity after 30 min at pH 3.0, and 75% activity after 30 min at pH 10.0 (Additional file 1: Figure S4b, S4d). The influence of different metal ions, EDTA and SDS is shown in P505-15 research buy Table 3. Co-action of PdcDE and PdcG Because PdcG was able to metabolize the product of PdcDE, the activities of both His6-PdcDE and His6-PdcG were assayed in one reaction mixture with HQ as the substrate. This was done spectrophotometrically by following the change of absorbance at 320 nm. At the beginning of the reaction, the absorbance at 320 nm rose continuously (Figure 7c), while no rising curve was observed in the negative control (data not shown). This indicated that 4-HS was generated in the reaction mixture containing both enzymes. After about 180 seconds, the absorbance plateaued, suggesting that the generation of 4-HS had reached a limit. NAD+ (the cofactor of PdcG) was then added to the reaction mixture to a final concentration of 0.05

mM to activate His6-PdcG. Upon addition of NAD+, the absorbance at 320 nm immediately decreased rapidly, and then leveled off. However, no such results were observed when His6-PdcG was omitted from the reaction or when His6-PdcDE was incubated with a crude cell extract of the non-induced BL21 strain Selleckchem GF120918 that harbored pdcF instead of His6-PdcG (data not shown). This confirmed that 4-HS was the product of His6-PdcDE acting on HQ, and that 4-HS was the substrate of the enzyme His6-PdcG. Enzymatic assays of MA reductase activity MA reductase is the common enzyme of the two PNP degradation pathways and uses NADH as a cofactor [22]. In the MA reductase (His6-PdcF) assay, the decrease in absorption at 340 nm was used to monitor the conversion of NADH to NAD+ (ε340 NADH = 6.3 mM-1 cm-1), which conversion reflects the activity of His6-PdcF. When purified His6-PdcF

was added to the assay mixture, there was significant oxidation of NADH (Figure 8a). However, no oxidation of NADH was observed when His6-PdcF was omitted from the reaction (Figure 8b). Thus, PdcF reduced MA to β-ketoadipate with NADH as a many cofactor. Figure 8 Enzyme activity assay of PdcF. (a) Absorbance at 340 nm in the absence of His6-PdcF; (b) Absorbance at 340 nm during oxidation of NADH by His6-PdcF. His6-PdcF was active over a temperature range of 20-70°C with an optimal activity at 40°C, and over a pH range of 5.0-9.0 with an optimum activity at pH 7.0 (Table 2, Additional file 1: Figure S5a, S5c). Its specific activity was calculated to be 446.97 Umg-1. Further, the purified enzyme retained 10% activity after 20 min at 60°C, 20% activity after 30 min at pH 3.0, and 58% activity after 30 min at pH 10.0 (Additional file 1: Figure S5b, S5d). The influence of different metal ions, EDTA and SDS is shown in Table 3. Discussion Pseudomonas sp.