## Cleavage of mutant collagens by MMP1, MMP2, and catalytic domain of MMP1 (MMP1(ΔC)).

A, cleavage kinetics of collagens by MMP1 in molecules with Cys for α1(I) Gly or Cys for α1(I) Arg substitutions. Each time point represents an average of two experiments. In one, the mutant labeled with Alexa Fluor 488 (AF488) was mixed with normal control labelled with Cy5 and treated with MMP1 within the same sample tube. In the other, the fluorescent labels were switched. The error bar represents the corresponding standard deviation. Gray circles show the kinetics of cleavage for disulfide bonded chains formed in molecules containing two α1(I) chains with Cys for Gly or Cys for Arg substitutions. B, relative cleavage rates for all studied mutants determined as the ratio of the initial cleavage rate of all α1(I) chains in the mutant to the initial cleavage rate of α1(I) chains in the normal control within the same sample tube. The initial cleavage rates were determined by linear regression of the first 3–4 data points in the kinetic experiments shown in A and similar experiments for the other mutants and enzymes. The cleavage rates of α1(I)-R780L with MMP1(ΔC) were not measured. The cleavage rates of all mutants were larger than in normal control with high statistical significance (*p*<0.001). For instance, the cleavage rate by MMP2 was 0.18±0.01 in α1(I)-R780L vs. 0.01±0.006 in NC (in the same units), yielding high statistical significance for (0.18±0.01)/(0.01±0.006) > 1 despite noticeable uncertainty in the absolute value of this ratio.