Updated FTP location. The cytochrome P450 limonene-6-hydroxylase (P450), cytochrome P450 reductase (CPR) and carveol dehydrogenase (CDH) were expressed in Escherichia coli for (−)-carvone production from (−)-limonene. The optimum ratio of enzyme expression to maximize (−)-carvone production was determined using the proteome analysis quantification concatamer (QconCAT) method.