Cysteine ultraviolet absorption

The ultraviolet absorption spectra of cysteine, cystine, and methionine are shown in Figs. 2, 3, and 11. The lowest energy (long-wave absorption band) transitions have been assigned (Mulliken, 1935 Walsh, 1953) as n — (f transitions. Transition assignments for disulfide spectra have been critically discussed in a recent paper by McGlynn et al. (1962). The... 

Lead bound to cysteine residues in proteins results in the appearance of several intense absorption bands in the ultraviolet (UV) region of the absorption spectrum (37, 50-53, 89, 90). These absorption bands have been used successfully in our laboratory and elsewhere to monitor the stability of lead-protein interactions (37, 53) (discussed in detail in Sections IV and VI) but there has not yet been a detailed study of the electronic origin of these bands. Here, we review previous work on the theory of CT transitions in related systems and then apply those ideas to the spectra observed for lead in proteins. 

---