Part of the heterotrimer that catalyzes the conversion of D-gluconate to 2-dehydro-D-gluconate. The role of this subunit in the heterotrimer is not known. A + D-gluconate = 2-dehydro-D-gluconate + AH2 Optimum pH is 5.0. Optimum temperature is 30 degrees Celsius. Heterotrimer. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has been experimentally proven.