Demonstration of SDF-1α and SDF-1β cleavage by human serum. Recombinant SDF-1α and SDF-1β were incubated for 20 hours at room temperature alone or with 10% normal human serum. (A) Mass spectrometry of recombinant SDF-1α after 20 hours of incubation at room temperature alone or with 10% normal human serum. (B) Mass spectrometry of recombinant SDF-1β after 20 hours of incubation at room temperature alone or with 10% normal human serum. The average molecular mass after deconvolution of the indicated ion peaks (left) is shown on the right. Representative experiments are shown.