STUDIES ON REDUCTION OF ELASTIN .2. EVIDENCE FOR PRESENCE OF ALPHA-AMINOADIPIC ACID DELTA-SEMIALDEHYDE AND ITS ALDOL CONDENSATION PRODUCT

Studies on the reduction of elastin with sodium borotritide have shown: (1) Most of the tritiated compounds in an acid hydrolysate of elastin previously reduced with sodium borotritide arise from modified lysine residues in the backbone of the peptide chains. This was confirmed by studies on [14C]lysine-labeled elastin obtained from chick embryo aortas grown in tissue culture. (2) Residues of α-aminoadipic acid δ-semialdehyde which are formed by the deamination of the ϵ-amino group of certain lysine residues in elastin, are reduced by sodium borohydride to ϵ-hydroxynorleucine residues. Hydrolysis of reduced elastin in 6 n HC1 leads to substantial conversion of the ϵ-hydroxynorleucine into ϵ-chloronorleucine, which in turn is converted into pipecolic acid upon treatment with dilute alkali. Studies on pure ϵ-hydroxynorleucine confirmed these results. It was also found that ϵ-hydroxynorleucine was stable to treatment with 2 n NaOH at 110° for 22 hr. Hydrolysis of reduced tritiated elastin in 2 n NaOH revealed 2-3 residues of ϵ-hydroxynorleucine/1000 amino acid residues. (3) The properties of the most prominent radioactive compound in an alkaline hydrolysate of reduced elastin were consistent with the reduced derivative of an aldol condensation product of two residues of α-aminoadipic acid δ-semialdehyde. Mass spectrum of its ethyl ester derivative, oxidation with a mixture of periodate and permanganate, hydrogenation over palladium, and the calculated specific activity all agree with the proposed structure. In elastin the aldol condensation product may serve a dual role: first, as an independent cross-link, and second as a precursor for the desmosine crosslinks. In bovine elastin, there are 4-5 residues of the aldol condensation product per 1000 amino acids. © 1969, American Chemical Society. All rights reserved.