These carefully controlled analytical conditions are compatible with routine operations, affording accurate and precise results for the more diagnostically relevant metabolites such as testosterone itself and the 5α- and 5β-androstanediols. The values of the TS-ERC pairs measured in reference populations are described and the results from the routine testing of several hundreds of athletes' samples are discussed. Robust, this technique permitted the detection of adverse findings that would have been missed had these low level metabolites not been analyzed.

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2,2 -Dichlorobiphenyl (CB) is transformed by the biphenyl dioxygenase of Burkholderia xenovorans LB400 (LB400 BPDO) into two metabolites (1 and 2). The most abundant metabolite, 1, was previously identified as 2,3-dihydroxy-2 -chlorobiphenyl and was presumed to originate from the initial attack by the oxygenase on the chlorine-bearing ortho carbon and on its adjacent meta carbon of one phenyl ring. 2,3,2 ,3 -Tetrachlorobiphenyl is transformed by LB400 BPDO into two metabolites that had never been fully characterized structurally. We determined the precise identity of the metabolites produced by LB400 BPDO from 2,2 -CB and 2,3,2 ,3 -CB, thus providing new insights on the mechanism by which 2,2 -CB is dehalogenated to generate 2,3-dihydroxy-2 -chlorobiphenyl. We reacted 2,2 -CB with the BPDO variant p4, which produces a larger proportion of metabolite 2. The structure of this compound was determined as cis-3,4-dihydro-3,4-dihydroxy-2,2 -dichlorobiphenyl by NMR. Metabolite 1 obtained from 2,2 -CB-d 8 was determined to be a dihydroxychlorobiphenyl-d 7 by gas chromatographic-mass spectrometric analysis, and the observed loss of only one deuterium clearly shows that the oxygenase attack occurs on carbons 2 and 3. An alternative attack at the 5 and 6 carbons followed by a rearrangement leading to the loss of the ortho chlorine would have caused the loss of more than one deuterium. The major metabolite produced from catalytic oxygenation of 2,3,2 ,3 -CB by LB400 BPDO was identified by NMR as cis-4,5-dihydro-4,5-dihydroxy-2,3,2 ,3 -tetrachlorobiphenyl. These findings show that LB400 BPDO oxygenates 2,2 -CB principally on carbons 2 and 3 and that BPDO regiospecificity toward 2,2 -CB and 2,3,2, ,3 -CB disfavors the dioxygenation of the chlorine-free orthometa carbons 5 and 6 for both congeners.The enzymes of the bacterial biphenyl catabolic pathway are very versatile. They can co-metabolically transform several polychlorinated biphenyls (1). The initial reaction of this pathway is catalyzed by the biphenyl dioxygenase (BPDO) 1 (2, 3). The cis- (2R,3S)-dihydroxy-1-phenylcyclohexa-4,6-diene (commonly called cis-2,3-dihydro-2,3-dihydroxybiphenyl) generated by the catalytic oxygenation of biphenyl is dehydrogenated by the 2,3-dihydro-2,3-dihydroxybiphenyl-2,3-dehydrogenase (BphB) and the catechol produced is cleaved by the 2,3-dihydroxybiphenyl-1,2-dioxygenase (BphC). The 2-hydroxy-6-oxo-6-phenyl-hexa-2,4-dienoic acid produced is then hydrolyzed by the 2-hydroxy-6-oxo-6-phenyl-hexa-2,4-dienoic acid hydrolase to yield benzoate and 2-hydroxypentanoate (Fig. 1). The substrate specificity of BPDO is crucial, because it limits the range of compounds that can potentially be degraded by the catabolic system. BPDO is a three-component enzymatic system (4 -6) (Fig. 1). The first component is an iron-sulfur protein (ISP BPH ) that interacts with the substrate to catalyze the addition of molecular oxygen. The second and third components are a flavoprotein reductase and a ferredoxin that are involved in the transfer of electrons from N...

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