2-Hydroxy-6-oxo-6-(2′-aminophenyl)-hexa-2,4- dienoic acid [6-(2′-aminophenyl)-HODA] hydrolase, involved in carbazole degradation by Pseudomonas resinovorans strain CA10, was purified to near homogeneity from an overexpressing Escherichia coli strain. The enzyme was dimeric, and its optimum pH was 7.0-7.5. Phylogenetic analysis showed the close relationship of this enzyme to other hydrolases involved in the degradation of monocyclic aromatic compounds, and this enzyme was specific for 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (6-phenyl-HODA), having little activity toward 2-hydroxy-6-oxohepta-2,4-dienoic acid and 2-hydroxymuconic semialdehyde. The enzyme had a Km of 2.51 μM and kcat of 2.14 (s−1) for 6-phenyl-HODA (50 mM sodium phosphate, pH 7.5, 25°C). The effect of the presence of an amino group or hydroxyl group at the 2′-position of phenyl moiety of 6-phenyl-HODA on the enzyme activity was found to be small; the activity decreased only in the order of 6-(2′-aminophenyl)-HODA (2.44 U/mg)>6-phenyl-HODA (1.99 U/mg)>2-hydroxy-6-oxo-6-(2′-hydroxyphenyl)-hexa-2,4-dienoic acid (1.05 U/mg). The effects of 2′-substitution on the activity were in accordance with the predicted reactivity based on the calculated lowest unoccupied molecular orbital energy for these substrates.
                                    2-羟基-6-氧代-6-(2'-
氨基苯基)-六-2,4-二烯酸[6-(2'-
氨基苯基)-H
ODA]
水解酶参与食
树脂假单胞菌菌株 CA10 的
咔唑降解,从过度表达的大肠杆菌菌株中纯化至接近同质。该酶为二聚体,其最适pH为7.0-7.5。系统发育分析表明该酶与参与单环芳香族化合物降解的其他
水解酶有密切关系,并且该酶对2-羟基-6-氧代-6-苯基六-2,4-二烯酸(6-苯基- H
ODA),对 2-羟基-6-氧七-2,4-二烯酸和 2-羟基粘康半醛几乎没有活性。对于 6-苯基-H
ODA(50 mM 
磷酸钠,pH 7.5,25°C),该酶的 Km 为 2.51 μM,kcat 为 2.14 (s−1)。发现6-苯基-H
ODA的苯基部分2'位上的
氨基或羟基的存在对酶活性的影响很小;活性降低的顺序为:6-(2'-
氨基苯基)-H
ODA (2.44 U/mg)>6-苯基-H
ODA (1.99 U/mg)>2-羟基-6-氧代-6-(2' -羟基苯基)-六-2,4-二烯酸(1.05 U/mg)。 2'-取代对活性的影响与基于计算的这些底物的最低未占据分子轨道能量所预测的反应性一致。