Proteolysis of human ELR⁺ CXC chemokines by MMP-1 and -9. (A) Tris-Tricine 15% SDS-PAGE gel analysis of MMP-1 and -9 cleavage of human CXCL1, -2, -3, -5, -6, -7, and -8. MMP-12 cleavage products are shown for comparison. Black horizontal lines separate individual gels. (B) Identification of human MMP-1 and -9 cleavage products by MALDI-TOF MS. Deconvolution of mass spectrometry data revealed that neither MMP-1 nor MMP-9 cleaved any of the human ELR⁺ CXC chemokines in the ELR motif. Arrows indicate MMP-1 or -9 cleavage sites. N/D, not determined.