The following diagram shows the biosynthesis of B12 coenzymes, starting with the vitamin....

The following diagram shows the biosynthesis of B12 coenzymes, starting with the vitamin. DMB is dimethylbenzimidazole.

(a) What one additional substrate or cofactor is required by enzyme B?

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(b) Genetic deficiency in animals of enzyme C would result in excessive urinary excretion of what compound?

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 (c) Some forms of the condition described in (b) can be successfully treated by injection of rather massive doses of vitamin Bl2. What kind of genetic alteration in the enzyme would be consistent with this result?

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 (d) Genetic deficiency in animals of enzyme B will result in excessive urinary excretion of what amino acid?