A ketohexose is a ketone-containing hexose (a six-carbon monosaccharide). The most common ketohexoses, each of which represents a pair of enantiomers (D- and L-isomers), include fructose, psicose, sorbose, and tagatose. Ketohexose is stable over a wide pH range, and with a primary pK_a of 10.28, will only deprotonate at high pH, so is marginally less stable than aldohexose in solution.