Figure 2.

Sequential scans of the X-ray absorption near-edge region of the thiol protease papain from papaya (Carica papaya). Papain contains seven cysteine residues, six of which are involved in three cystine disulfide linkages. The spectra show the characteristic disulfide double peak close to 2470 eV, with the spectrum of oxidized forms (sulfates and sulfonates) appearing near 2480 eV with increasing exposure to the beam. Data were measured at room temperature in 1 M bis-tris buffer at pH 7.0 on SSRL beamline 6-2.