A study of three-component fitting of protein circular dichroism spectra

Abstract

1. 1. The linear fitting of protein circular dichroism (CD) spectra in the region of peptide absorption with basis spectra for helical, β-sheet and unordered structure is critically examined by matrix rank analysis, factor analysis and least-squares fitting of the CD spectra of five proteins of known structural composition—myoglobin, lysozyme, ribonuclease, lactate dehydrogenase and papain—and five CD spectra of a protein of unknown structure—bovine erythrocuprein. The rationale of the numerical methods is given. 2. 2. The two groups of CD spectra are shown by matrix rank analysis and factor analysis to have a three-component basis within error limits acceptable as experimental error. The basis spectra are also shown by matrix rank analysis to be the same or closely similar in the two groups of spectra. 3. 3. The fitting of the erythrocuprein CD spectra with empirical, statistically average basis spectra for helical, β-sheet and unordered structure derived from the CD spectra of myoglobin, lysozyme, ribonuclease, lactate dehydrogenase and papain is therefore considered to be acceptable, and a tentative interpretation of the secondary structure in bovine erythrocuprein is made. 4. 4. Three-component fitting of protein CD spectra is considered to be justifiable.