Vitamins Problem Set

B₁₂/Folate Problem set

Question 4: A second reaction requiring B₁₂

Tutorial to help answer the question

Buildup of which metabolite in serum is a specific indicator of a vitamin B₁₂ deficiency?

A. methylmalonic acid

B. methylmalonyl CoA

C. N⁵-methyl THF

D. methionine

E. succinyl CoA

Tutorial

The methylmalonic aciduria connection

Fig. 4 - Buildup of methylmalonate and propionyl CoA in B₁₂ deficiency

Methylmalonyl CoA mutase catalyzes one of only two known B₁₂-requiring reactions, and the only one to occur in mitochondria. B₁₂ must first be converted to its adenosyl-B₁₂ form before it can serve as a cofactor for this enzyme. Disruption of this reaction leads directly to methylmalonic aciduria, with associated neurological symptoms and learning deficiencies. A contributing factor may be a secondary backup of propionyl CoA which may substitute for acetyl CoA in the citrate synthase reaction to form methyl citrate, a TCA cycle poison. Presumably, this scenario is particularly serious for neural tissue due to its high oxidative demands. Now on to folate metabolism...

The Biology Project
The University of Arizona
January 31, 2000
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B12/Folate Problem set

Question 4: A second reaction requiring B12

Tutorial

B₁₂/Folate Problem set

Question 4: A second reaction requiring B₁₂