<prompt> Essential pentosuria can occur due to deficiency in metabolic pathway ofUronic acidHexose-mono-phosphateGlycogenFructose  <response>: Ans. a Uronic acid Ref. Harpers Biochemistry-26thpg. 105, 163, 170; 27thpg. 177Glucuronic acid is synthesized from glucose via the uronic acid pathway, of major significance for the excretion of metabolites and foreign chemicals xenobiotics as glucuronides. A deficiency in the pathway leads to essential pentosuria. Considerable quantities of L-xylulose appear in the urine because of absence of the enzyme necessary to reduce L-xylulose to xylitol. Parenteral administration of xylitol may lead to oxalosis, involving calcium oxalate deposition in brain and kidneys.URONIC ACID PATHWAY In liver, uronic acid pathway catalyzes conversion of glucose to glucuronic acid, ascorbic acid, pentoses. It is also an alternative oxidative pathway for glucose, but--like the pentose phosphate pathway--it does not lead to the generation of ATP. Glucose 6-phosphate is isomerized to glucose 1-phosphate, which then reacts with uridine triphosphate UTP to form uridine diphosphate glucose UDPGlc in a reaction catalyzed by UDPGlc pyrophosphorylase, as occurs in glycogen synthesis. UDPGlc is oxidized at carbon 6 by NAD-dependent UDPGlc dehydrogenase in a two-step reaction to yield UDP-glucuronate.Deficiencies in the enzymes of fructose and galactose metabolism lead to essential fructosuria and the galactosemias. 