centrifugation and washing with 10-mmol EDTA until a neutral pH was reached, the samples were digested twice with bacterial collagenase (Sigma type 7, 125 U per 100 mg tissue, Sigma-Aldrich, Taufkirchen, Germany) for 24 h at 37°C. At the end of each collagenase digestion, the samples were rinsed thoroughly in cold aqua dest. and digested by trypsin (133 μg per 1 mg tissue) for 18 h at 37°. Finally the samples were rinsed in distilled water, washed in 8-M urea/ 0.1 M mercaptoethanol for 18 h at room temperature, rinsed in aqua dest., freeze-dried, weighed for the calculation of elastin yield, and stored at −20°C until further processing