Keto-enol tautomerism is a very significant process in biochemistry. The means in biochemistry of interconversion of an aldose, such as glucose, to a ketose, such as fructose, occurs via their common enolate isomer. For example, the isomerization of the 6-phosphate ester of D-glucose to D-fructose by way of keto-enol tautomerism occurs as one of the first steps of glycolysis. Additionally, a similar isomerization occurs a few steps later to convert the ketose dihydroxyacetone phosphate to glyceraldehyde 3-phosphate.