A yeast deletion library was screened based on NADH fluorescence using a 384-well plate assay to identify a yeast isolate lacking a previously identified cell surface oxidase exhibiting an oscillatory pattern with a period length of 25 min and resistant to the ENOX1-specific inhibitor simalikalactone D (YNOX for yeast-specific ENOX = ENOX4). The cDNA was cloned from a yeast over expression library using NADH fluorescence analyzed by Fast Fourier transform and decomposition fits. The objective was to identify and sequence an ENOX homologue in Saccharomyces cerevisiae with a 25 min rather than a 24 min period length (YNOX). The finding identified YDR005C as the yeast ENOX protein with a temperature-independent 25 min period length and insensitive to inhibition by simalikalactone D. The encoded protein was expressed in bacteria and characterized. Gel slices corresponding to 55 kDa and 39 kDa His-tagged proteins exhibited 25 min oscillatory patterns not inhibited by 1 μM simalikalactone D for both NADH oxidation and reduced coenzyme Q10?oxidation as well as a protein disulfide-thiol interchange activity which alternated with the oxidative activities. Activities were phased by low-frequency electromagnetic fields but, in contrast, to yeast ENOX1, not by addition of melatonin. The assay in the presence of D2O shifted the length of the oscillatory period from 25 min to 32 min. The YDR005C deletion mutant cells lacked the ENOX4 clock output present in the wild type yeast.