Abstract
Four phenylacetaldehyde dehydrogenases (designated as FeaB or StyD) originating from styrene-degrading soil bacteria were biochemically investigated. In this study, we focused on the Michaelis-Menten kinetics towards the presumed native substrate phenylacetaldehyde and the obviously preferred co-substrate NAD+. Furthermore, the substrate specificity on four substituted phenylacetaldehydes and the co-substrate preference were studied. Moreover, these enzymes were characterized with respect to their temperature as well as long-term stability. Since aldehyde dehydrogenases are known to show often dehydrogenase as well as esterase activity, we tested this capacity, too. Almost all results showed clearly different characteristics between the FeaB and StyD enzymes. Furthermore, FeaB from Sphingopyxis fribergensis Kp5.2 turned out to be the most active enzyme with an apparent specific activity of 17.8 ± 2.1 U mg-1. Compared with that, both StyDs showed only activities less than 0.2 U mg-1 except the overwhelming esterase activity of StyD-CWB2 (1.4 ± 0.1 U mg-1). The clustering of both FeaB and StyD enzymes with respect to their characteristics could also be mirrored in the phylogenetic analysis of twelve dehydrogenases originating from different soil bacteria.
Highlights
Aldehyde dehydrogenases (ALDHs, EC 1.2.1) comprise a huge group of enzymes occurring in every organism ranging from bacteria and fungi to invertebrates and mammals [1]
R. opacus 1CP [39] and P. putida S12 [2] harbor the “classic” sty operon with the order of the sty genes identically to the enzymatic cascade—the styrene monooxygenase (SMO) is encoded by styA and styB, the styrene oxide isomerase (SOI) by styC, and the phenylacetaldehyde dehydrogenases (PADs) by styD
The fatty aldehyde dehydrogenase (FADH) of R. opacus 1CP was used as outgroup based on the “summary tree of ALDH families” shown previously [1]
Summary
Aldehyde dehydrogenases (ALDHs, EC 1.2.1) comprise a huge group of enzymes occurring in every organism ranging from bacteria and fungi to invertebrates and mammals [1]. The thiol group of cysteine is activated via deprotonation by the glutamate residue and binds temporarily to the carbonyl C of the substrate. Thereby, it supports the elimination of a hydride from the carbonyl C. Glutamate deprotonates a water molecule in the step and a hydroxide ion is formed This ion can attack the carbonyl C as a nucleophile leading to an organic acid as product.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
