Provided is 5-oxoprolinase which can be used suitably in use applications such as the improvement of umami taste of a food or beverage, the separation of an optical isomer from a racemic body and the quantification of L-pyroglutamic acid.5-Oxoprolinase originated from a microorganism belonging to the genus Aspergillus； and a 5-oxoprolinase gene encoding the 5-oxoprolinase. The 5-oxoprolinase according to the present invention can be collected from a culture which is produced by culturing a microorganism containing the 5-oxoprolinase gene or a microorganism capable of producing the 5-oxoprolinase in a culture medium.5-Oxoprolinase can be provided, which is less likely to be affected by the change in a pH value compared with known enzymes, can be used in a broad pH range, can fully act in an intermediate temperature range in which the 5-oxoprolinase is highly stable, and has high affinity for substrates. The 5-oxoprolinase according to the present invention has such an advantageous property that the 5-oxoprolinase is highly safe in food/beverage processing use, because the 5-oxoprolinase is originated from a microorganism belonging to the genus Aspergillus which has long eating experience.L'invention concerne la 5-oxoprolinase qui peut être utilisée de façon appropriée dans des applications d'utilisation telles que l'amélioration du goût umami d'un aliment ou d'une boisson, la séparation d'un isomère optique à partir d'un corps racémique et la quantification d'acide L-pyroglutamique. L'invention concerne la 5-oxoprolinase ayant pour origine un microorganisme appartenant au genre Aspergillus ； et un gène de 5-oxoprolinase codant pour la 5-oxoprolinase. La 5-oxoprolinase selon la présente invention peut être collectée à partir d'une culture qui est produite par la culture d'un microorganisme contenant le gène 5-oxoprolinase ou un microorganisme apte à produire la 5-oxoprolinase dans un milieu de culture. La 5-oxoprolinase peut être fournie, laquelle est moins suscep
