Reductive dechlorination of DDT by haem proteins

Nothing lasts forever: understanding microbial biodegradation of polyfluorinated compounds and perfluorinated alkyl substances

Poly- and perfluorinated chemicals, including perfluorinated alkyl substances (PFAS), are pervasive in today's society, with a negative impact on human and ecosystem health continually emerging. These chemicals are now subject to strict government regulations, leading to costly environmental remediation efforts. Commercial polyfluorinated compounds have been called 'forever chemicals' due to their strong resistance to biological and chemical degradation. Environmental cleanup by bioremediation is not considered practical currently. Implementation of bioremediation will require uncovering and understanding the rare microbial successes in degrading these compounds. This review discusses the underlying reasons why microbial degradation of heavily fluorinated compounds is rare. Fluorinated and chlorinated compounds are very different with respect to chemistry and microbial physiology. Moreover, the end product of biodegradation, fluoride, is much more toxic than chloride. It is imperative to understand these limitations, and elucidate physiological mechanisms of defluorination, in order to better discover, study, and engineer bacteria that can efficiently degrade polyfluorinated compounds.

Reactions between iron porphyrins and tetrahydropterins

Data from the last few years have revealed a novel biological role of the tetrahydrobiopterin ( H 4 B ) cofactor, in one-electron transfers to the heme of the active site of NO-synthases (NOSs) with intermediate formation of a H 4 B -derived radical. These electron transfers play a key role in the catalytic cycles of the two steps catalyzed by NOS, the N ω-hydroxylation of L-arginine, and the three-electron oxidation of N ω-hydroxyarginine to L-citrulline and NO. Recent experiments performed between various tetrahydropterins and iron porphyrins have shown that the one-electron transfer from tetrahydropterins, such as the natural cofactors H 4 B and tetrahydrofolate or the synthetic 6,7-dimethyltetrahydropterin (diMeH4P), to Fe(III) porphyrins of sufficiently high redox potentials (> about -100 mV versus NHE for the Fe(III)/Fe(II) couple) is a very general reaction that occurs with formation of a tetrahydropterin-derived radical. Reaction of diMeH4P with a stable porphyrin Fe(II)-O 2 complex leads to a diMeH4P-derived radical and a transient Fe(III)-OOH complex, mimicking the reaction between H 4 B and heme Fe(II)-O 2 in the NOS catalytic cycle. Tetrahydropterins such as diMeH4P also reduce hemeproteins Fe(III) of sufficiently high redox potentials, such as cytochromes c and b5 or metmyoglobin, to the corresponding hemeproteins Fe(II) .

Biodehalogenation: reactions of cytochrome P-450 with polyhalomethanes

The products, stoichiometry, and kinetics of the oxidation of the enzyme cytochrome P-450 cam by five polyhalomethanes and chloronitromethane are described. The reactivity of the enzyme is compared with that of deuteroheme and with the enzyme in its native cell, Pseudomonas putida (PpG-786). In all cases, the reaction entails hydrogenolysis of the carbon-halogen bond: 2FeIIP + RCXn----2FeIIIP + RCHXn-1 (P = porphyrin or P-450 cam in vitro and in vivo). Trichloronitromethane was the fastest reacting substrate, and chloroform was the slowest. The results establish that P. putida is a valid whole cell model for the reductase activity of the P-450 complement in these reactions. The reactions of cytochrome P-450 with polyhaloalkanes proceed in a manner quite analogous to other iron(II) proteins in the G conformation. The chemistry observed for the enzyme parallels that of its iron(II) porphyrin active site. Iron-bonded carbenes are not intermediates, and hydrolytically stable iron alkyls are not products of these reactions.