Acid hydrolysis cobalamins

NO adds reversibly to reduced cobalamin, Cbl(II).156 It does not react directly with aquacobalamin(III), (0blni(H2O)), but it does add to Cbl,n(N02 ) and Cblm(NO).175 Acid hydrolysis of the dinitroso species releases nitrite, and binding of nitrite to Cblln(H20) generates Cbln,(. 02 ). This sequence thus affords a nitrite-catalyzed mechanism for NO substitution at Cblln(H20). The reaction of NO with Com porphyrins is quite complex.176 In the first step, NO displaces an axial water ligand to form a weakly bound mono NO complex this mono NO complex reacts with a second molecule of NO to form nitrite and a reduced Co-NO complex. This latter process is called reductive nitrosylation. Manganese(II) porphyrins bind NO very rapidly.177 Stability constants have been measured for the formation of mono and bis NO complexes of Cun(dithiocarbamate)2.157... 

Paper chromatography is one of the earlier techniques for the separation of cobal-amins and corrinoids. Whatman nr.2 paper with xcc-butanol/glacial acetic acid/ water (100 3 50) (10) or n-butanol/isopropanol/water (10 7 10) (11) is most frequently used. Whatman 3MM paper has been found useful for the separation of acid hydrolysis products of cyanocobalamin using 2-butanol/glacial acetic acid/water (440 4.1 150) with 0.07% KCN as the ascending solvent (79). A similar system was applied by Kolhouse and Allen (80) for the preparation of various cobalamin analogs and by Kondo et al (81) for the analytical separation of analogs from animal tissues. 

HPLC has proven to be very useful in the preparation of p-tri-n-butylstan-nyl hippurate conjugates to cobalamin-diaminododecane adducts, which themselves were prepared after linking diaminododecane to the isolated free b-, d-, and e-carboxylate products of mild acid hydrolysis of cobalamin (112). The final purpose of this study was the preparation of a radioiodinated cobalamin analog, capable of binding to transcobalamin n and traceable in mice or rats. With a similar aim in mind Pathare et al. (113) studied the possibilities to prepare bioactive biotinylated cobalamin analogs. 

The combination of this radical with the Bi2r species generates a new alkyl cobalamin with the substrate as ligand. We have thus accomplished a transalkylation of the cobalt atom. How does the Co—C bond become activated toward homolytic cleavage It is believed that the presence and proper orientation of the propionamide side chains on the corrin ring are responsible for the ease of the enzymatic system, possibly by some distortion of the corrin (269). Support for this hypothesis comes from the fact that hydrolysis of a side chain to the corresponding acid results in an inactive coenzyme Bi2 molecule. It is not known why nature proceeds by homolytic fission, a unique situation in coenzyme chemistry ... 

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