Candida tropicalis ATCC 20336 can grow on fatty acids or alkanes as its sole source of carbon and energy, but strains blocked in ␤-oxidation convert these substrates to long-chain ␣,-dicarboxylic acids (diacids), compounds of potential commercial value (Picataggio et al., Biotechnology 10:894-898, 1992). The initial step in the formation of these diacids, which is thought to be rate limiting, is -hydroxylation by a cytochrome P450 (CYP) monooxygenase. C. tropicalis ATCC 20336 contains a family of CYP genes, and when ATCC 20336 or its derivatives are exposed to oleic acid (C 18:1 ), two cytochrome P450s, CYP52A13 and CYP52A17, are consistently strongly induced (Craft et al., this issue). To determine the relative activity of each of these enzymes and their contribution to diacid formation, both cytochrome P450s were expressed separately in insect cells in conjunction with the C. tropicalis cytochrome P450 reductase (NCP). Microsomes prepared from these cells were analyzed for their ability to oxidize fatty acids. CYP52A13 preferentially oxidized oleic acid and other unsaturated acids to -hydroxy acids. CYP52A17 also oxidized oleic acid efficiently but converted shorter, saturated fatty acids such as myristic acid (C 14:0 ) much more effectively. Both enzymes, in particular CYP52A17, also oxidized -hydroxy fatty acids, ultimately generating the ␣,-diacid. Consideration of these different specificities and selectivities will help determine which enzymes to amplify in strains blocked for ␤-oxidation to enhance the production of dicarboxylic acids. The activity spectrum also identified other potential oxidation targets for commercial development.

A rapid enzymatic fluorometric assay for measuringd-arabinitol in serum was developed using recombinantd-arabinitol dehydrogenase from Candida albicans (rArDH). rArDH was produced in Escherichia coli and purified by dye-ligand affinity chromatography. rArDH was highly specific for d-arabinitol, cross-reacting only with xylitol (4.9%) among all polyols tested. A Cobas Fara II centrifugal autoanalyzer (Roche) was used to measure NADH fluorometrically when rArDH and NAD were added to serum extracts, andd-arabinitol concentrations were calculated from standard curves derived from pooled human serum containing known amounts ofd-arabinitol. The method was precise (mean intra-assay coefficients of variation [CVs], 0.8%, and mean interassay CVs, 1.6%) and rapid (3.5 min per assay) and showed excellent recovery of added d-arabinitol in serum (mean recovery rate, 101%). The mean and median d-arabinitol/creatinine ratios were 2.74 and 2.23 μM/mg/dl, respectively, for the 11 patients with candidemia compared to 1.14 and 1.23 μM/mg/dl, respectively, for 10 healthy controls (P < 0.01). These results confirm earlier studies showing that serum d-arabinitol measurement may help to promptly diagnose invasive candidiasis. The technique shows a significant improvement in terms of accuracy, cost, simplicity, specificity, and speed compared with gas chromatography, mass spectrometry, and earlier enzymatic assays.