Porphyrins and Bile Pigments MCQs

Option A: Van den Bergh Reaction: Quantitation of bilirubin employs a colorimetric method based on the reddish-purple color formed when bilirubin reacts with diazotized sulfanilic acid. An assay conducted in the absence of added methanol measures "direct bilirubin," which is bilirubin glucuronide. An assay conducted in the presence of added methanol measures total bilirubin. The difference between total bilirubin and direct bilirubin is known as "indirect bilirubin," and is unconjugated bilirubin. Option B: Ehrlich's Reaction is used to detect urobilinogen in urine. Option C: Schlesinger's Reaction is used to detect urobilin. Option D: Fouchet's Reaction is used to detect bile pigment like bilirubin in urine.

Mutations in the gene encoding enzyme ALA synthase cause X-linked Sideroblastic anemia. It leads to anemia with decreased red cell counts and hemoglobin. Heme biosynthesis is initiated by the condensation of succinyl-CoA and glycine in a pyridoxal phosphate-dependent reaction catalyzed by mitochondrial δ-aminolevulinate synthase (ALA synthase. Succinyl-CoA + glycine → δ-aminolevulinate + CoA-SH + CO2 Humans express two isozymes of ALA synthase. ALAS1 is ubiquitously expressed throughout the body, whereas ALAS2 is expressed in erythrocyte precursor cells. Formation of δ-aminolevulinate is rate-limiting for porphyrin biosynthesis in mammalian liver. So Option A is correct.

Ans. is 'a' i.e.,ALA synthase [Ref Harper's 29' le p. 309] Heme synthesis takes place in all cells, but occurs to greatest extent in bone marrow and liver. The first step in the synthesis of heme is the condensation of glycine and succinyl Co-A to form 6- aminolevulinic acid (6-ALA), which occurs in mitochondria. This reaction is catalyzed by 6-ALA synthase which requires pyridoxal phosphate (PLP) as cofactor. This is the rate limiting step in heme synthesis.

Ans. is 'a' i.e.,Uroporphyrinogen I synthase [Ref Harper 29tVe p. 313]