Question

propane-1,2-diol reaction with HCN​

Answer 1

Answer:

The early observation that addition of propane-1,2-diol to the complex of DDH and adenosylcobalamin led to the transient formation of cob(II)alamin provided the first evidence for the direct chemical participation of coenzyme B12 in catalysis.21 In the same study, another reaction leading to cleavage of coenzyme B12 by DDH was suicide inactivation by glycolaldehyde.

Hydrated glycolaldehyde is an analogue of the substrate propane-1,2-diol, and it reacts with the complex of DDH and adenosylcobalamin to form cob(II)alamin, 5′-deoxyadenosine, and the glycolaldehyde radical shown in Figure 6.22,56,57 The reaction proceeds by direct hydrogen transfer from glycolaldehyde to 5-deoxyadenosine, as proven by reaction of [2-3H]glycolaldehyde to form 5′-deoxy-[3H]adenosine (P. A. Frey, unpublished results). The formation of cob(II)alamin and 5′-deoxyadenosine is observed spectrophotometrically and in 14C-tracer experiments,21,22 and the glycolaldehyde radical is observed by EPR.56,57 The carbon atoms of glycolaldehyde as well as 5′-deoxyadenosine and cob(II)alamin remain tightly bound to the enzyme in the inactivated complex. The highly delocalized electron in the glycolaldehyde radical lends it such stability that it is neither able to react further nor to revert to glycolaldehyde and adenosylcobalamin. The resulting complex is inactive