Microbial glutaminase: Biochemistry, molecular approaches and applications in the food industry

Glutaminase is widely distributed in microorganisms including bacteria, yeast and fungi. The enzyme mainly catalyzes the hydrolysis of γ-amido bond of L-glutamine. In addition, some enzymes also catalyze γ-glutamyl transfer reaction. A highly savory amino acid, L-glutamic acid and a taste-enhancing amino acid of infused green tea, theanine can be synthesized by employing hydrolytic or transfer reaction catalyzed by glutaminase. Therefore, glutaminase is one of the most important flavor-enhancing enzymes in food industries. In this review, subsequent to a discussion on the definition of glutaminase, the enzymatic properties, applications of glutaminase in the food industry, and occurrence and distribution of the enzyme are described. We then illustrate the gene cloning, primary structure, and 3D-structure of glutaminase. Finally, to facilitate the future applications of glutaminase in food fermentations, the mechanisms of action of salt-tolerant glutaminase are briefly discussed.