Essential pentosuria can occur due to deficiency in metabolic pathway of

Ans. a (Uronic acid) (Ref. Harper's Biochemistry-26th/pg. 105, 163, 170; 27th/pg. 177)Glucuronic 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.