News used to reveal characteristics not apparent from conventional studies of enzymes that have strong electronic coupling with the electrode and are capable of displaying high rates of substrate turnover. The degree to which an enzyme is biased to catalyze more effectively in one direction can be quantified, and the ability Resolution of SDH from Complex II and adsorption of SDH onto to scan across a conthe electrode surface. tinuous potential range allows detection of small changes in electron-transis biased to catalyze fumarate reduction port activity that occur as sites switch (reversal of the tricarboxylic acid cycle) at pH values below 7.7. The authors con- between redox states. (J. Am. Chem. Soc. 1996,118, 5031-38.) cluded that electrochemistry can be
A transient metabolite in the field
munity during the sample processing. Analysis by GC/MS was completed within 12 h. The researchers found the intermediate in all the samples collected within the contaminant plume; the intermediate was absent in the negative controls. (Environ. Sci. Technol. 1996,30, 2099-103.)
Observation of an intermediary metabolite provides strong evidence that biodegradation of an environmental contaminant is taking place. If that metabolite is unstable, identifying it is complicated, because prior to analysis, microorganisms respond quickly to changes arising from removal from the contaminated field site. As a result, studies relying on the identification of an unstable intermediary metabolite to document in situ realtime biodegradation are rare. Mark S. Wilson and Eugene L. Madsen of Cornell University have reported the field identification of l,2-dihydroxy-l,2-dihydronapthalene (1,2-DHDN), a transient intermediate in the biodegradation of napthalene, which is a component of several pollutant mixtures, including coal tars and crude oil. Using solid-phase extraction and GC/MS, the authors determined 1,2DHDN in waters flowing though a contaminated site. To minimize sample artifacts, a field laboratory was set up and collection, extraction, and derivatization steps were completed within Mass spectra of authentic 1,2-DHDN (top) 30 min. In addition, several steps were compared with the metabolite formed in an taken, such as adding the respiratory enriched culture inoculated with a mixture of inhibitor sodium azide, to avoid chang- site-derived microorganisms (middle) and ing the native aquatic microbial comcollected in waters on site (bottom). 462 A
Analytical Chemistry News & Features, August 1, 1996
Interatomic distance measurements by NMR Knowledge of interatomic distances is important in correlating the observed function of materials with their structure. Although traditional methods of determining interatomic distances, such as crystallography and solution-state NMR, can provide information on atomic location with accuracies of 0.5-2.0 A, these methods are time-consuming and are not always representative of in vivo conformation. K. T Mueller of The Pennsylvania State University and T. P. Jarvie and G. T Went of CuraGen Corp. have used rotational-echo double-resonance (REDOR), anew analysis method for solid-state NMR, to study biologically relevant molecules. They performed the REDOR experiment on a mixture of two small cyclic peptides bound to mBHA resin via the terminal Gly. The two peptides were identical except for their labeling; one peptide was labeled with 15N,1-13C Gly and the other with 15N,2-13C Gly. To obtain a spectrum of the dipolar coupling present in the peptide system, a REDOR transform was applied to the dephasing data. The results agreed well with X-ray crystallographic data from pure Gly. The authors believe that the REDOR transform has the potential to aid in the drug discovery process via improved local structural studies of regions of peptides that bind proteins. (J. Am. Chem. Soc. 1996,118,5330-31.)
Two effective MALDI matrices Matrix-assisted laser desorption/ionization MS (MALDI-MS) allows the analysis of large biomolecules. Commonly used matrices include a-cyano-4-hydroxycinnamic acid (ce-CHCA), sinapinic acid (SA), and 2,5-dihydroxybenzoic acid (DHB). David M. Lubman and co-workers at The University of Michigan evaluated three structurally related compounds, 4-hydroxy-3-me-
