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Adenosyltransferase: an enzyme and an escort for coenzyme B12?

Trends in biochemical sciences (2005-06-14)
Mamoru Yamanishi, Monica Vlasie, Ruma Banerjee
ABSTRACT

Many organic cofactors are both rare and reactive. They are usually in low abundance, which poses problems for efficient collision-based targeting to dependent enzymes, whereas their reactivity is problematic for side reactions. Sequestration and escorted delivery presents one solution to this conundrum, but such porters, if they exist, are mostly unknown. In humans, the mitochondrial enzyme methylmalonyl-coenzyme A mutase uses coenzyme B(12) (adenosylcobalamin) but would be inactive if bound to the cofactor precursor that is delivered to the mitochondrion. Adenosyltransferase converts cob(II)alamin to coenzyme B(12). Based on kinetic evidence for interaction between the two enzymes, the 40-fold greater affinity for coenzyme B(12) and the higher coordination number for cobalt in the mutase, we propose that the adenosyltransferase is a dual-function protein: an enzyme that synthesizes coenzyme B(12) and a chaperone that delivers it.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Vitamin B12a hydrochloride, ≥96% (UV), ≥96% (HPLC)
Sigma-Aldrich
Methylcobalamin, vitamin B12 analog
Sigma-Aldrich
Coenzyme B12, ≥97.0%
Sigma-Aldrich
Hydroxocobalamin acetate, vitamin B12 analog
Sigma-Aldrich
Vitamin B12, ≥98%