Abstract
The present work deals with the reactions between cobalamins and water-miscible aldehydes under aerobic and anaerobic conditions. When 10ml of aqueous solution containing about 1×10^<-4> mole of aldehyde and 3.2×10^<-7> moles of aquocobalamin was shaken in the air at 35℃, about 10^<-5> mole of carboxylic acid was produced after 100hrs. On the contrary, the use of cyanocobalamin instead of aquocobalamin did not cause any detectable oxidation of aldehyde. From these results, it is obvious that aquocobalamin acts as the catalyst in the oxidation of aldehyde by oxygen molecules. Under anaerobic conditions, aquocobalamin was reduced to vitamin B_<12r> by adding aldehyde. In this case, the formation of vitamin B_<12r> was more rapid as pH-value of the solution was higher and was remarkably promoted by irradiation. The reaction also occured much more easily in iso-propanol than in water, but retarded in the presence of acetone. These facts suggested the following mechanism. Under anaerobic conditions : 1) Aldehyde coordinates to the Co-atom in exchange for H_2O of aquocobalamin. 2) Proton leaves from the aldehyde-cobalamin complex. 3) The unstable intermediate thus formed splits to give an acyl radical and vitamin B_<12r>. And under aerobic conditions : 4) The acyl radical is attacked by oxygen molecule and converted to carboxylic acid. 5) Vitamin B_<12r> is reoxidized to aquo-cobalamin.
