The biosynthesis of desmosine and isodesmosine.

The biosynthesis of desmosine and isodesmosine was studied with chick embryo aortas in tissue culture. Radioactivity was incorporated into desmosine and isodesmosine when uniformly labeled lysine-W was added to the medium, but no activity could be incorporated into these amino acids from aspartic acidJ4C, glutamic acidJ4C, or threonine-14C. The labeled desmosine and isodesmosine obtained after the incorporation of radioactivity from lysine-r4C were subjected to the action of strong sodium hydroxide solutions. This treatment liberates the pyridinium nitrogen along with its side chain in the form of lysine. The lysine thus liberated from the labeled desmosine or isodesmosine was found to contain one-fourth of the total activity of the parent compound. The distribution of radioactivity in the carboxyl carbons of these compounds was also studied. These results strongly support the hypothesis that 4 lysine molecules condense to form 1 desmosine or isodesmosine molecule.