Why fructose metabolised more rapidly than glucose?

Answer 1

In comparison with glucose or galactose metabolism, fructose is metabolized at a faster rate which results in an increased rate of glycolysis. This is because fructose bypasses the enzyme phosphofructokinase-1 (PFK-1) which is the rate limiting step (RLS) of glycolysis which results in rapid metabolism through the glycolytic pathway. PFK-1 (the RLS of glycolysis) converts fructose-6-phosphate to fructose-1,6-bisphosphate.

Fructose enters the glycolytic pathway beyond the RLS (fructose-> fructose-1-phosphate->dihydroxyacentone (DHAP, a glycolytic intermediate) <--> glyceraldehyde--> glyceraldehyde-3-phosphate->->->-> enters glycolytic pathway to produce pyruvate beyond the RLS. Also hexokinase (initial enzyme of glycolysis converting glucose to glucose-6-phospahte) can metabolize a small amount of fructose (fructose--> fructose-6-phosphate). It is a way in which some fructose enters glycolytic pathway.