Rat tail collagen type I was gelled at 2 mg/ml and incubated at 37 °C for 24 hours with enzymes in 12.5 mM Na PO4 buffer, pH 7.5. Lane: 1) 0.75 μg MMP-1; 2) 1.5 μg MMP-1; 3) 1.5 μg MMP-1, 20 Mm EDTA; 4) 0.75 μg MMP-1, 20 mM EDTA, 15 μg APCE; 5) 1.5 μg MMP-1, 20 mM EDTA, 15 μg APCE; 6) 1.5 μg MMP-1, 15 μg APCE. Digests were reduced and analyzed by 4–12% SDS-PAGE. Where present, the ~97 kDa band is either APCE or rFAP.