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Comparison of Alkyl Hydroperoxide Reductase (AhpR) and Water‐Forming NADH Oxidase from Lactococcus lactis ATCC 19435
Author(s) -
Jiang Rongrong,
Riebel Bettina R.,
Bommarius Andreas S.
Publication year - 2005
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200505063
Subject(s) - chemistry , nox , lactococcus lactis , oxidase test , peroxidase , biochemistry , bacteria , enzyme , lactic acid , organic chemistry , combustion , biology , genetics
We have successfully applied the sequence comparison‐based approach to develop a peroxidase (gene AhpC) and a water‐forming NADH oxidase from Lactococcus lactis ( L. lactis ). We found a considerably lower maximum specific activity of nox‐1 (AhpF) (15 U/mg) from L. lactis compared to its nox‐2 counterpart (95 U/mg). Both nox‐1 and nox‐2 are turnover‐limited, as expected for enzymes with labile, redox‐active thiols in the active site. In the absence of exogenously added thiols, both nox‐1 and nox‐1/peroxidase are considerably more stable against overoxidation than nox‐2: the total turnover number TTN is 82,000 for nox‐1 and nox‐1/peroxidase vs. 39,000 for nox‐2. Addition of exogenous thiols, however, increases nox‐2 stability by a factor of two, up to the level of nox‐1. Kinetic and stability analysis does not reveal any clear advantage for oxygen scavenging via the nox‐1 or the nox‐2 routes in lactic acid bacteria. Expression levels in lactic acid bacteria upon exposure to oxidative stress rather than kinetic performance more likely account for the previously observed superiority of nox‐2 effectiveness over nox‐1.