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A Fragment from the Constant Portion of IgG Obtained by Peptic Digestion at High Temperatures¹

From the Department of Immunology Research, Roswell Park Memorial Institute, ² Buffalo, New York 14203

Abstract

Two myeloma IgG immunoglobulins and normal human IgG immunoglobulin were digested with pepsin at various temperatures for various times. After digestion at temperatures exceeding 60°C, all the proteins studied showed a distinctive anodic arc which had not been observed after digestion at 37°C. An immunoglobulin fragment corresponding to this arc was isolated from the peptic digests of the myeloma immunoglobulins and the normal immunoglobulin by gel filtration on a Sephadex G-150 column. The amino acid compositions of these high temperature fragments from the three immunoglobulins were as consistent as the compositions of the constant portions of different IgG molecules.

Sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis of the reduced fragment of IgG (Col) showed only two bands. That of normal human IgG showed two strong bands at the identical positions to the two bands of IgG (Col), in addition to a weak third band. The molecular weights of these two bands correspond to the approximate size of a domain, i.e., 12,000 and 14,000. An immunodiffusion experiment indicated that the high temperature fragment was derived from the constant portions of light and heavy chain. This fragment sedimented as a single symmetrical peak with a s_20,w value of 3.3 in pH 8.6 Veronal buffer (ionic strength 0.10). It appears to be a new fragment which has not yet been reported.

Footnotes

¹ This work was supported in part by Grant AI-3962 from the National Institute of Allergy and Infectious Diseases.

² A unit of the New York State Department of Health.