elastin A fibrous protein that is the major constituent of the yellow elastic fibres of connective tissue. It is rich in glycine, alanine, proline, and other nonpolar amino acids that are cross-linked, making the protein relatively insoluble. Elastic fibres can stretch to several times their length and then return to their original size. Elastin is particularly abundant in elastic cartilage, blood-vessel walls, ligaments, and the heart.

elastin Insoluble protein in connective tissue, which is not affected by cooking; the cause of tough meat.

elastin (i-lasst-in) n. protein forming the major constituent of elastic tissue fibres.