Question

Many foods contain high fructose corn syrup.  Why does this lead to metabolic syndrome?   What regulatory step in glycolysis is bypassed?

Answer 1

Answer-Fructose, a simple sugar which present in fruits and honey and is responsible for their sweet taste.After it is ingested, sucrose is degraded inside the gut by enzyme sucrase, which release fructose and glucose that are then absorbed. In addition to sucrose, other major source of fructose is high fructose corn syrup (HFCS).which consists of fructose and glucose mixed in a variety of concentrations, but most commonly as 55% fructose and 45% glucose. HFCS and sucrose are the major sources of fructose in the diet, and HFCS is a major ingredient present in , desserts, and various processed foods Despite the similarity in their chemical structures, fructose and glucose are metabolized in completely different ways and utilize different GLUT transporters.Number of other furanose sugars can also act as KHK substrates,KHK-A has a higher Km for fructose (7 mmol/L) ,which leads to metabolic syndrome.High fructose consumption induces insulin resistance and other manifestations of metabolic syndrome

Steps bypassed-In the liver, fructose bypasses the two highly regulated steps of glycolysis, catalyzed by glucokinase/hexokinase/phosphofructokinase all of which are inhibited with increasing concentrations of their byproducts. Instead, fructose enters the pathway at a level which is not regulated and is metabolized to fructose-1-phosphate primarily by fructokinase or ketohexokinase (KHK) (Figures 1 and 2). Fructose may also be metabolized by hexokinase; however, the Km for fructose is much higher than glucose, and hence minimal amounts of fructose are metabolized via this pathway