Oxidizing heterologous expression

Ruiz-Duenas FJ, Martinez MJ, Martinez AT (1999) Heterologous expression of Pleurotus eryngii peroxidase confirms its ability to oxidize Mn(2+) and different aromatic substrates. Appl Environ Microbiol 65 4705-4707... 

This red species has also been shown to form in the reaction of reduced enzyme with DMSO (Adams et at., 1999), and appears to represent a kinetically viable DMSO Michaelis complex, which rapidly achieves equilibrium with the eorresponding Eox DMS species in the enzyme active site. Consistent with this, recent kinetic work with DMSO reductase has demonstrated that the enzyme is kinetically competent to oxidized DMS as well as reduce DMSO (Adams et al., 1999). Interestingly, the former reaction is sensitive to extended preincubation of enzyme with DMS under aerobic (but not anaerobic), but the latter reaction is not. The spectrum of the DMS-modified enzyme resembles that exhibited by recombinant as-isolated enzyme heterologously expressed in E. coli, which can be converted to native enzyme by reduction and reoxidation (Hilton et al.,... 

ItxB codes for an unusual cytochrome P-450 monooxygenase that was implicated in the oxidation and cyclization of the tryptophan moiety, while ItxD encodes an oxidoreductase that is putatively involved in the oxidation of 34 to 35 and 36. The sequence of ItxC was not similar to any characterized gene product, and thus it was believed to be involved in the prenylation of 34. The LtxC protein was heterologously expressed in... 

Figure 9 Type III PKS biosynthesis In myxobacteria. Biosynthesis of flaviolin (20) catalyzed by a type III PKS (CHS) from Sorangium cellulosum So ce56. The primary product released from the CHS, 1,3,6,8-tetrahydroxynaphthalene (26), Is spontaneously oxidized to form 20. Neither 26 nor 20 has been Identified In the myxobacterial strain. Indicating that the CHS-encodIng gene Is silent under the tested conditions. Activation of the type III PKS-encodIng gene by heterologous expression In Pseudomonas putida led to the formation of the red pigment 20 In the P. putida CHS strain (see picture).

However, the relevance of these transformations to retinoic acid homeostasis in target tissues is not clear. White et probed a panel of mRNAs from mammalian cell lines with a cDNA from a zebrafish P450 shown to be involved in retinoic acid-inducible retinoic acid oxidation and characterized P450 26A1 (ref [1391]). The heterologously expressed enzyme converted all-traws-retinoic acid to the 4-hydroxy-, and 4-oxo-, and 18-hydroxy products. The turnover numbers are unknown because the amount of P450 was not quantified, but the enzyme is clearly able to catalyze the oxidation of sub-p,M additions of all-fraris-retinoic acid. Apparently other retinoic acid isomers are not substrates. 

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