Fructose catabolism

Fructose occurs naturally in foods as a free monosaccharide and as a component of the disaccharide sucrose. It is also widely used as a sweetener. In the body, fructose catabolism occurs in the liver and to a lesser extent in the kidney and small intestine. In these tissues, it is converted to dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate, two intermediates in the glycolytic pathway, in a sequence of three reactions. It is phosphorylated to form fructose 1-phosphate, which is cleaved by aldolase to yield dihydroxyacetone phosphate and D-glyceraldehyde, and the latter compound is phosphorylated to yield D-glyceraldehyde 3-phosphate. Other pathways exist for the conversion of D-glyceraldehyde to intermediates of glycolysis, but these appear to play only a minor role in normal fructose metabolism (Sillero et al. 1969).

果糖作为一种游离的单糖存在于多种食物中，同时也是二糖蔗糖的组成部分。此外，果糖作为甜味剂的应用亦极为广泛。在人体内，果糖的代谢主要在肝脏进行，肾脏和小肠亦有一定程度的代谢。在这些组织中，果糖经过一系列三步反应，转化为二羟丙酮磷酸和D-甘油醛-3-磷酸，这两者均为糖酵解途径的中间产物。果糖首先被磷酸化形成果糖-1-磷酸，随后由醛缩酶裂解，生成二羟丙酮磷酸和D-甘油醛，而后者进一步磷酸化，最终生成D-甘油醛-3-磷酸。此外，存在其他途径将D-甘油醛转化为糖酵解的中间产物，但这些途径在正常的果糖代谢中似乎仅扮演次要角色（Sillero et al. 1969）。