The Escherichia coli fadK (ydiD) Gene Encodes an Anerobically Regulated Short Chain Acyl-CoA Synthetase (2004)

We recently reported a new metabolic competency for Escherichia coli, the ability to degrade and utilize fatty acids of various chain lengths as sole carbon and energy sources (Campbell, J. W., Morgan-Kiss, R. M., and Cronan J. E. (2003) Mol. Microbiol. 47, 793–805). This β-oxidation pathway is distinct from the previously described aerobic fatty acid degradation pathway and requires enzymes encoded by two operons, yfcYX and ydiQRSTD. The yfcYX operon (renamed fadIJ) encodes enzymes required for hydration, oxidation, and thiolytic cleavage of the acyl chain. The ydiQRSTD operon encodes a putative acyl-CoA synthetase, ydiD (renamed fadK), as well as putative electron transport chain components. We report that FadK is as an acyl-CoA synthetase that has a preference for short chain length fatty acid substrates (<10 C atoms). The enzymatic mechanism of FadK is similar to other acyl-CoA synthetases in that it forms an acyl-AMP intermediate prior to the formation of the final acyl-CoA product. Expression of FadK is repressed during aerobic growth and is maximally expressed under anaerobic conditions in the presence of the terminal electron acceptor, fumarate. We recently reported a new metabolic competency for Escherichia coli, the ability to degrade and utilize fatty acids of various chain lengths as sole carbon and energy sources (Campbell, J. W., Morgan-Kiss, R. M., and Cronan J. E. (2003) Mol. Microbiol. 47, 793–805). This β-oxidation pathway is distinct from the previously described aerobic fatty acid degradation pathway and requires enzymes encoded by two operons, yfcYX and ydiQRSTD. The yfcYX operon (renamed fadIJ) encodes enzymes required for hydration, oxidation, and thiolytic cleavage of the acyl chain. The ydiQRSTD operon encodes a putative acyl-CoA synthetase, ydiD (renamed fadK), as well as putative electron transport chain components. We report that FadK is as an acyl-CoA synthetase that has a preference for short chain length fatty acid substrates (<10 C atoms). The enzymatic mechanism of FadK is similar to other acyl-CoA synthetases in that it forms an acyl-AMP intermediate prior to the formation of the final acyl-CoA product. Expression of FadK is repressed during aerobic growth and is maximally expressed under anaerobic conditions in the presence of the terminal electron acceptor, fumarate. Acyl-CoA synthetases (more properly called fatty acid:CoA ligases or acyl-CoA ligases) perform key roles in metabolic and regulatory processes by activating free fatty acids to their CoA thioesters. The enzymatic mechanism is a two-step reaction that proceeds via the intermediate formation of an acyl-adenylate (acyl-AMP) intermediate: step 1, fatty acid + ATP → fatty acyl-AMP + PPi and step 2, fatty acyl-AMP + CoA → fatty acyl-CoA + AMP. Acyl-CoAs serve as important intermediates in diverse metabolic functions, such as fatty acid transport, β-oxidative degradation of fatty acids, and phospholipid biosynthesis, as well as enzyme activation, cell signaling, and transcriptional regulation (1Faergeman N.J. Knudsen J. Biochem. J. 1997; 323: 1-12Crossref PubMed Scopus (587) Google Scholar). Consistent with the diverse roles of acyl-CoA synthetases (ACSs) 1The abbreviations used are: ACS, acyl-CoA synthetase; MOPS, 3-(N-morpholino)propanesulfonic acid; fad, fatty acid degradation; FACS, fatty acid CoA-ligase; RB, rich broth; HPLC, high performance liquid chromatography; TES, 2-{[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]amino}-ethanesulfonic acid. in cell metabolism, many eukaryotic organisms encode several different ACSs that specifically activate short (C6–C8), medium (C10–C12), long (C14–C20), or very long (>C22) chain length fatty acids (1Faergeman N.J. Knudsen J. Biochem. J. 1997; 323: 1-12Crossref PubMed Scopus (587) Google Scholar, 2Fujino T. Man-Jong K. Minekura H. Suzuki H. Yamamoto T.T. J. Biochem. (Tokyo). 1997; 122: 212-216Crossref PubMed Scopus (22) Google Scholar). Moreover, some organisms possess multiple enzymes for each set of acyl chain lengths. In contrast, only a single ACS called FadD has been reported in Escherichia coli, although, multiple ACS isoforms of varying molecular masses recently shown to be artifacts of proteolysis (3Yoo J.H. Cheng O.H. Gerber G.E. Biochem. J. 2001; 360: 699-706Crossref PubMed Google Scholar) had been reported (4Kameda K. Imai Y. Biochim. Biophys. Acta. 1985; 832: 343-350Crossref PubMed Scopus (9) Google Scholar, 5Samuel D. Estroumza J. Ailhaud G. Eur. J. Biochem. 1970; 12: 576-582Crossref PubMed Scopus (30) Google Scholar). E. coli FadD has been purified to homogeneity (6Black P.N. DiRusso C.C. Metzger A.K. Heimert T.L. J. Biol. Chem. 1992; 267: 25513-25520Abstract Full Text PDF PubMed Google Scholar, 7Kameda K. Nunn W.D. J. Biol. Chem. 1981; 256: 5702-5707Abstract Full Text PDF PubMed Google Scholar) and has a broad substrate specificity for fatty acids of medium and long chain lengths. Activation of long chain fatty acids to their acyl-CoA thioesters is required not only for aerobic degradation of the acids, but also for induction of the fad (fatty acid degradation) genes that catalyze the degradation process. In the absence of long chain acyl-CoAs, the FadR regulatory protein binds to its operator sequences, where it functions as a repressor of transcription of the fad genes (and as a transcriptional activator of the fabA and fabB fatty acid biosynthetic genes) (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar, 9Henry M.F. Cronan Jr., J.E. Cell. 1992; 70: 671-679Abstract Full Text PDF PubMed Scopus (125) Google Scholar, 10Cronan Jr., J.E. Subrahmanyam S. Mol. Microbiol. 1998; 29: 937-943Crossref PubMed Scopus (102) Google Scholar). However, in the presence of long chain acyl-CoAs, FadR is released from the fad operators and transcription of these genes is induced. Acyl-CoAs of 10 or fewer acyl carbon atoms cannot release FadR from the operator sites and thus the aerobic degradative pathway is not induced and the acids cannot be utilized for growth. However, when FadR is inactivated by mutation these strains can utilize medium chain length fatty acids as the sole carbon source (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar, 9Henry M.F. Cronan Jr., J.E. Cell. 1992; 70: 671-679Abstract Full Text PDF PubMed Scopus (125) Google Scholar, 10Cronan Jr., J.E. Subrahmanyam S. Mol. Microbiol. 1998; 29: 937-943Crossref PubMed Scopus (102) Google Scholar). ACSs belong to a larger family of AMP-forming enzymes, which include firefly luciferase, acetyl-CoA synthetases, and nonribosomal peptide synthetases (11Babbitt P.C. Kenyon G.L. Martin B.M. Charest H. Slyvestre M. Scholten J.D. Chang K.H. Liang P.H. Dunaway-Mariano D. Biochemistry. 1992; 31: 5594-5604Crossref PubMed Scopus (189) Google Scholar, 12Chang K.H. Xiang H. Dunaway-Mariano D. Biochemistry. 1997; 36: PubMed Scopus Google Scholar, E. T. J. 1997; PubMed Scopus Google Scholar, Chem. Biol. PubMed Scopus Google of which an acyl-adenylate intermediates in their reaction The of of family to and possess a of (11Babbitt P.C. Kenyon G.L. Martin B.M. Charest H. Slyvestre M. Scholten J.D. Chang K.H. Liang P.H. Dunaway-Mariano D. Biochemistry. 1992; 31: 5594-5604Crossref PubMed Scopus (189) Google Scholar). ACSs an the fatty acid P.N. DiRusso C.C. Microbiol. Mol. Biol. 2003; PubMed Scopus Google Scholar, J.D. DiRusso C.C. R. P.N. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). putative and as well as the been to FadD P.N. DiRusso C.C. Microbiol. Mol. Biol. 2003; PubMed Scopus Google Scholar, J.D. DiRusso C.C. R. P.N. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). of these in a cleavage that from proteolysis with of enzymatic by (3Yoo J.H. Cheng O.H. Gerber G.E. Biochem. J. 2001; 360: 699-706Crossref PubMed Google Scholar). reported that that E. coli can utilize fatty acids as sole carbon sources during growth under anaerobic conditions that an electron is in the medium (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). This anaerobic β-oxidation pathway is distinct from the previously aerobic pathway in a of are: that several of the fad enzymes and required for the aerobic pathway not required for anaerobic growth fatty acids, the anaerobic fatty acid pathway is not under the of the of the aerobic fad and fatty acids of different chain lengths utilized by the two (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). We two putative of several fad enzymes, yfcYX and ydiQRSTD. The yfcYX operon encodes putative for and (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). The ydiQRSTD operon several that also a in anaerobic from the genes encode a putative a that and these to a and two and that to a electron transport that to is also a putative acyl-CoA of the of the ydiQRSTD The encoded by the genes high to encoded by the operon of anaerobic K. J. 1998; PubMed Google and as the electron transport chain the β-oxidation of fatty acids with the chain. The of putative operon is which and to encode an ACS (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). This the that FadK can be with the FadD its length with many and and the to fatty acids under aerobic or anaerobic conditions (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google fatty acids under anaerobic that FadK FadD under anaerobic However, to long chain fatty acids (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar, G. Eur. J. Biochem. PubMed Scopus Google Scholar, M. E. Mol. PubMed Scopus Google Scholar) and thus the of FadK to FadD under aerobic conditions to of FadK or to of enzyme We report that FadK is an ACS that is short chain fatty FadK is not expressed under aerobic growth The enzyme is expressed under anaerobic but the of the terminal electron fatty acids from Acyl-CoA fatty acids, and other from and to M. J. Biol. Chem. Full Text PDF Google Scholar) and Chem. 12: Google from The from and and medium with medium and medium medium J.H. in Scholar) with acids and G. Mol. Microbiol. 2001; PubMed Google Scholar). aerobic growth and used of and when growth acids with and with and used final of in aerobic or in anaerobic with or fumarate. in a anaerobic in a anaerobic an of and as previously described (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). of and strains of E. coli and from D. PubMed Scopus Google Scholar) by the of and S. PubMed Scopus Google Scholar) The from and the from via or The used to the of or with the or by or for strains or The the encoded the PubMed Scopus Google Scholar). by of the from The mutation by the of to as a sole carbon with and other as described previously (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google D. PubMed Scopus Google PubMed Scopus Google S. PubMed Scopus Google in a new used in in a new of FadK and and genes of via under conditions set for and set for The purified via and The of the to the of the of the with and the and to with the enzymes to of the the of with the of or in and of the and of the protein of FadD and FadK during the genes with a a the and S. PubMed Scopus Google Scholar) for from the of The a by a This by to of to the of or the as well as to the of the S. PubMed Scopus Google Scholar). The to to of to the of the of the the of the S. PubMed Scopus Google Scholar). The set used to the and set used to the of the by not and Expression and of and with or or in with an of and induced with for The by for 10 The in and for The of the enzymes, for prior to the of of 10 and and of the via The for and of acid to the The for and the a and with of The protein by of TES, and The or The of the via 1970; PubMed Scopus Google Scholar). of the purified enzyme in a two of for 10 and prior to for Acyl-CoA synthetase by the in the Biochem. PubMed Scopus Google Scholar). as a in the presence of The very to the presence of to enzyme in prior to and the presence of in enzyme as well as other reaction by the in the absence of The ACS reaction fatty of and of the substrate to a the in the presence of a and prior to for 10 prior to enzyme to for of to be the reaction by the of of and the reaction for The in a In the of PPi during the reaction by the in a reaction in of the enzyme for Acyl-CoA used to the formation of from acids the of and Nunn K. Nunn W.D. J. Biol. Chem. 1981; 256: 5702-5707Abstract Full Text PDF PubMed Google Scholar). a reaction S. J. Biol. Chem. Full Text PDF PubMed Google Scholar) 10 fatty and enzyme and for FadK and The for and of a for of the acyl-CoA prior to the by the reaction by the of of by The free fatty acid by with The in a to of fatty acyl-CoA fatty acyl-AMP when CoA from the a S. Cronan Jr., J.E. J. 1998; PubMed Google Scholar). The and by a of and for by an with a ACS also via The reaction as described that the reaction to of the reaction for with acid and a The in for to R. D. PubMed Scopus Google Scholar). by the to for to and from cell or the and for by by for in The an protein and an a by to for The in and The with an in the with a with the by of the in and FadK to ACS The of acetyl-CoA synthetase Biochemistry. 2003; PubMed Scopus Google Scholar) reported of prior (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar) for the of two ACS called a called and that in FadK The is in the acyl-adenylate intermediate and is in of acyl-adenylate and that FadK is an ACS, as had (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). called that a called is also in However, the acyl-adenylate as previously the forms a in acetyl-CoA synthetase that binds the in the reaction Biochemistry. 2003; PubMed Scopus Google Scholar). FadK only of the of the P.N. DiRusso C.C. Microbiol. Mol. Biol. 2003; PubMed Scopus Google Scholar) that the of the of the 10 of in the the the is the FadK C as in other ACSs not these prior in (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google it that FadK an However, the and specificity of the enzyme to be purified FadK to homogeneity and the enzyme with E. coli a well and of the ACS and of FadK and FadD FadK for ACS two genes forms of the protein and two sites of in a of not and thus the by genes that encoded the or the a FadD with an also that of the forms of FadK and FadD in The purified to homogeneity of the had masses of a the molecular masses of the it that these of the The of the ACS of the purified used an that the of and The of that of had of Moreover, in the the of with protein when protein not This with the that reaction of during the reaction of the protein not that the the used in of or in of that the FadK under these conditions not that the is to be the used in be with and thus be to as utilized for the of the The of and also not had the synthetase to to the of of the as well as fatty acid chain length of the of and Nunn K. Nunn W.D. J. Biol. Chem. 1981; 256: 5702-5707Abstract Full Text PDF PubMed Google Scholar) used to the The of when CoA or ATP from the of in the absence of CoA This is to the of the of or of the of by had medium or long chain fatty acids and maximally and substrates In contrast, the with fatty acid substrates of carbon atoms in with K. Nunn W.D. J. Biol. Chem. 1981; 256: 5702-5707Abstract Full Text PDF PubMed Google for the and ACS in a new of and Acyl-CoA the of an from the We the with the FadD in the presence of and required of the substrate to In contrast, a substrate for in that only of the to In with the not and the enzyme that However, FadK acyl-CoA In the presence of and other required reaction a that had the as an in the presence of and CoA We also the acyl-CoA synthetase in the absence of CoA to the acyl-AMP with FadK and FadD to the of acyl-AMP these not well of during not used K. R. Eur. J. Biochem. PubMed Scopus Google Scholar) to for of the acyl-AMP The reaction from or in the presence or absence of CoA In the absence of enzyme the substrate in the absence of CoA FadK a an of as for an acyl-adenylate K. R. Eur. J. Biochem. PubMed Scopus Google Scholar). However, when CoA to the reaction the of the to the of an acyl-CoA R. D. PubMed Scopus Google Scholar). when as a fatty acid FadK formation of of and in the presence or absence of that the FadK proceeds via the acyl-AMP intermediate to the acyl-CoA product. In contrast, in the absence of FadD to of formation of when CoA to the reaction However, when the substrate and for and of or to the fatty the and and to formation not that these enzymes to the acyl-AMP intermediate from of the of purified and The fatty acid substrates or and in the presence or absence of of 2, and and 10 2, and CoA in the other The the of the where fatty acids R. D. PubMed Scopus Google Scholar) to of the acyl-adenylate by the in the fatty acid of FadK and previously reported that of FadK can a only during growth under anaerobic conditions (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). The of FadK to growth of under aerobic conditions be the of enzymatic in the presence of or of FadK during aerobic growth. it that FadK has ACS under aerobic conditions in and and the and to the of FadK these a that encodes a FadK expressed the similar in a called also had a growth when the fatty acids that the presence of the not enzyme of in medium in the presence or absence of or short long chain fatty The by and the and by by by with an that a peptide and also the only of in aerobic under conditions and and under anaerobic conditions but the of with the terminal electron In the presence of protein under growth conditions and in the presence of in the high under growth conditions In to the electron also the growth which the anaerobic growth of repressed in the presence of and induced in the presence of or However, in of of the growth medium used to only a of of the growth conditions However, when the protein purified from the of by acid of a protein not it that under the conditions used for the of the of and during anaerobic growth. or under anaerobic conditions in the presence of or as terminal electron in medium with or or via and with the to and The as described in the to of the of terminal electron and growth of and and and of strains the and or in the presence of and in the presence or absence of or The for the cell by the the by the The of the from of The to of the purified protein has been previously shown that FadD is by the to and a (3Yoo J.H. Cheng O.H. Gerber G.E. Biochem. J. 2001; 360: 699-706Crossref PubMed Google thus it that FadK also be specifically by However, of an mutation the in the cleavage of the of not Moreover, of cell to from the (3Yoo J.H. Cheng O.H. Gerber G.E. Biochem. J. 2001; 360: 699-706Crossref PubMed Google Scholar) also to the cleavage not that cleavage of FadK is of other We also under the growth conditions by of a that encoded a the C of the protein as described has been previously reported that is during DiRusso C.C. T. J. PubMed Google Scholar) and thus from and aerobic growth two in of which the the for the protein with the C and However, the only in the the to be the previously reported to be the of proteolysis (3Yoo J.H. Cheng O.H. Gerber G.E. Biochem. J. 2001; 360: 699-706Crossref PubMed Google Scholar). This in by the absence of the in a the as well as an mutation not growth in the presence of the long chain fatty in a of protein to in the absence of fatty acids C and and In contrast, had of protein when in the presence or absence of fatty acids The of repressed of the growth C and and and of a short chain fatty acid also for the for aerobic growth by of the well with previously with a DiRusso C.C. T. J. PubMed Google Scholar). the regulation of the fad enzymes during anaerobic also FadD in under anaerobic In to only of in the of under anaerobic of the growth medium used and In the of the source of terminal electron used to growth. In repressed in the presence of and to be induced by the presence of in the presence or absence of the fatty acids FadD in in in the presence of The protein of the of in growth with or during but when in the presence of the FadD in the in the and a of also also by (3Yoo J.H. Cheng O.H. Gerber G.E. Biochem. J. 2001; 360: 699-706Crossref PubMed Google Scholar) and it is that the is an We recently reported that E. coli has the ability to a of fatty acid substrates as sole carbon and energy sources the presence of an terminal electron such as or (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). these with that the β-oxidative fatty acid degradation pathway not under anaerobic conditions S. S. PubMed Scopus Google not that a of the is and is with fatty We that several E. coli fad in aerobic growth fatty acids fatty acids under anaerobic conditions and thus it that an pathway in anaerobic fatty acid The enzymatic for a β-oxidation pathway are: enzymatic of free fatty acids to their CoA thioesters to the of the acyl several enzymatic the that in thiolytic cleavage of the and the by β-oxidation to the chain. described in the two operons, yfcYX and to encode a set of enzymes for the anaerobic β-oxidative The of the ydiD (renamed fadK), encoded the putative the and but ACS not We also that FadK a preference for short chain length fatty acids strains to short chain fatty acids (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar) and the only very short chain substrates K. R. Eur. J. Biochem. PubMed Scopus Google Scholar). the short chain preference of that the ACS a similar specificity for chain length a by in of purified The substrate specificity of FadK that short and medium chain length fatty acids in where E. coli acids be from the of the or be the of of chain acids by other FadK is in of the of In the presence of fatty acids, and the by FadK or FadD is fatty However, when CoA from the reaction FadK the formation of of acyl-AMP intermediate when a short or a long chain acid as the fatty acid The of enzyme to acyl-AMP intermediate that FadK forms an acyl-AMP as has been previously for FadD P.N. DiRusso C.C. Microbiol. Mol. Biol. 2003; PubMed Scopus Google Scholar, M. E. Mol. PubMed Scopus Google Scholar). In contrast, in FadD an acyl-AMP intermediate only when a long chain fatty acid This that the short chain is not from by the FadD but is released free where it FadK to a for the medium chain acyl-AMP intermediate and the intermediate from that FadK is a ACS This be an of the enzyme or of the that purified and FadK as a protein it is However, FadD anaerobic growth of a a mutation in the presence of (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar). FadD is expressed under these conditions and is a substrate for enzyme K. Nunn W.D. J. Biol. Chem. 1981; 256: 5702-5707Abstract Full Text PDF PubMed Google Scholar) it that only of ACS required for anaerobic fatty acid FadK a with high to a chain acyl-CoA synthetase S. G. Biochim. Biophys. Acta. 2001; PubMed Scopus Google Scholar) that of the the that be in substrate specificity Consistent with FadD with However, that the has a substrate The acetyl-CoA synthetase Biochemistry. 2003; PubMed Scopus Google Scholar) to be the the and of the and Biochemistry. 2003; PubMed Scopus Google Scholar) that the a to the This is to the CoA for the of the of the and that the However, very recently a family of enzymes to be FadD by to acyl-CoA thioesters R. D. PubMed Scopus Google Scholar). enzymes, called the fatty acyl-AMP the acyl of the intermediate to of for the of these to catalyze of CoA to fatty acids, their and The is that the of to been from the of the fatty acyl-AMP to be or not the of can fatty acyl-AMP ligases from fatty acyl-CoA However, it that these two in the of the of fatty acyl-AMP ligases two with a single cleavage the the of several fatty acyl-CoA ligases from the to distinct cleavage R. D. PubMed Scopus Google Scholar). We shown that the of FadK to FadD under aerobic conditions of the of FadK and FadD a for and to The of that the not with the of the of for the long chain required to the fad is the of In the be via a This the for the of FadD and FadK and the of of of the had (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar) only of expressed under aerobic conditions of the carbon source or the of growth during anaerobic growth FadK expressed when as a terminal electron acceptor, but expressed in the presence of that the electron transport chain for of the during anaerobic β-oxidative degradation of fatty acids utilize fumarate. prior (8Campbell J.W. Morgan-Kiss R.M. Cronan Jr., E.J. Mol. Microbiol. 2003; 47: 793-805Crossref PubMed Scopus (155) Google Scholar) where cell growth the of the that is used as a carbon source as well as a electron the is encoded in an operon several putative and in an electron transport it is to that transcriptional regulation of the operon be by the presence of the terminal electron FadK only as a in the that it be a has been in which FadD is with the P.N. DiRusso C.C. Microbiol. Mol. Biol. 2003; PubMed Scopus Google Scholar). In the presence of long chain fatty acids in FadD in an in the absence of the the enzyme has a and is P.N. DiRusso C.C. Microbiol. Mol. Biol. 2003; PubMed Scopus Google Scholar). However, in the of the presence or absence of the the FadD only in the of The only FadD the cleavage (3Yoo J.H. Cheng O.H. Gerber G.E. Biochem. J. 2001; 360: 699-706Crossref PubMed Google Scholar). strains fatty acids not FadD cleavage by is not of of regulation P.N. DiRusso C.C. Microbiol. Mol. Biol. 2003; PubMed Scopus Google Scholar) cannot the of FadD in and the of or that other regulatory to be We and J. for of their anaerobic