The circular dichroism (C.D.) spectrum of C-reactive protein in the 200- to 240-nm region indicates that the protein has a) a considerable content of α-helix, a feature not found in immunoglobulins, and, b) a very similar structure to amyloid P component. In the 240- to 320-nm region the two proteins have different CD spectra, and show little resemblance to the phosphorylcholine-binding murine myeloma proteins such as MOPC 167 IgA. Removal of calcium from C-reactive protein produced a large change in the 240- to 320-nm region attributable to tyrosine, and addition of phosphorylcholine produced a small change in the same region. Inhibition of the reaction of C-reactive protein with pneumococcal C substance by analogs of phosphorylcholine showed that C-reactive protein is much more specific for the phosphate moiety than the myeloma proteins. Despite these structural and binding-site differences, comparison of the amino-acid sequences of C-reactive protein and the hypervariable regions of the myeloma proteins suggests that the phosphorylcholine-binding sites of the two may still have features in common.

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