Catalytic subunit of the NovJ(2)K(2) heterotetramer that catalyzes the NADPH-dependent reduction of the tyrosyl moiety of L-beta-OH-Tyr-S-NovH intermediate to yield the tethered beta-ketotyrosyl-S-NovH in the novobiocin biosynthesis pathway. Novobiocin is an aminocoumarin family antibiotic that targets bacterial DNA gyrases. Antibiotic biosynthesis; novobiocin biosynthesis. Heterotetramer; the NovJ(2)K(2) heterotetramer is composed of subunits of 2 NovJ and 2 subunits of NovK. Belongs to the short-chain dehydrogenases/reductases (SDR) family.