Valyl-alanyl-prolyl-glycine (VAPG) serves as a quantitative marker for human elastins.

Thermolysin digests of human elastins were examined for reliable elastin peptide markers as determined by HPLC followed by amino acid sequencing of promising peaks. The tetrapeptide VAPG was found to occur in the early portion of the chromatogram in a highly reliable fashion. The peptide appears to be significantly amplified, when compared with the other peptides, in that it is derived from the hexapeptide repeat in elastin, VGVAPG, which repeats itself in two three-piece segments in the c-terminal portion of the tropoelastin molecule. VAPG serves as a highly reliable quantitative measure for human elastins, allowing sensitivities to less than a microgram. Thus, it is a significantly more accurate measure than other existing methods. Precision also appears to be enhanced because of the directness of the measurement. The use of VAPG as a quantitative marker for human elastin has clinical application in the study of elastin-based connective tissue diseases.