The actual biological function of YdiB remains unclear, nor is it known whether 3-dehydroshikimate or quinate represents the natural substrate. Catalyzes the reversible NAD-dependent reduction of both 3-dehydroshikimate (DHSA) and 3-dehydroquinate to yield shikimate (SA) and quinate, respectively. It can use both NAD or NADP for catalysis, however it has higher catalytic efficiency with NAD. L-quinate + NAD(+) = 3-dehydroquinate + H(+) + NADH L-quinate + NADP(+) = 3-dehydroquinate + H(+) + NADPH NADP(+) + shikimate = 3-dehydroshikimate + H(+) + NADPH NAD(+) + shikimate = 3-dehydroshikimate + H(+) + NADH Metabolic intermediate biosynthesis; chorismate biosynthesis; chorismate from D-erythrose 4-phosphate and phosphoenolpyruvate: step 4/7. Homodimer. Belongs to the shikimate dehydrogenase family. Truncated C-terminus.