Flourescence and Absorption Studies of Limulus Hemocyanin and Its Components
The absorption spectrum of a deoxygenated hemocyanin is in general a typical protein spectrum. Upon binding oxygen, hemocyanin exhibits a profound change in the absorption spectrum. Shaklai and Daniel (1970), in studying the fluorescence of Levantina hierosolima, reported that when the hemocyanin is deoxygenated, or when copper is removed, the fluorescence yield at pH 6.6 increases four fold in each case. The quenching on oxygen binding is traced to radiationless energy transfer from the tryptophanyl residues to the Cu…o groups. Bannister and co-workers (Bannister and Wood, 1971; Bannister et al., 1973) reported that for Murex trunoulus the fluorescence is attributable to tryptophan, and the fluorescence is enhanced by 513 per cent when the apohemocyanin is prepared. Since there are significant differences between hemocyanins from molluscs and arthropods, including differences in molecular architecture as revealed by electron microscopy, circular dichroism, and subunit dissociation properties (Sullivan et al., 1974), we have carried out fluorescence and absorption studies using Limulus,an arthropod hemocyanin, and the results are presented in this paper. The choice of this hemocyanin takes on medical significance because Limulus lysate is now extensively investigated for rapid endotoxin assay (Sullivan and Watson, 1974).
KeywordsTryptophan Residue Fluorescence Yield Horseshoe Crab Component Versus Sodium Sulfite
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