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Bence Jones Proteins and Light Chains of Immunoglobulins

XIII. Effect of Elastase-like and Chymotrypsin-like Neutral Proteases Derived from Human Granulocytes on Bence Jones Proteins^1,2,

University of Tennessee Memorial Research Center and the East Tennessee Cancer Research Center, University of Tennessee Center for the Health Sciences, Knoxville, Tennessee 37920, and the Medical Clinic, University of Marburg, Marburg, West Germany

Abstract

Bence Jones proteins can be cleaved specifically by several types of endopeptidases into fragments corresponding to the amino-terminal, variant (V_L) portion and to the carboxyl-terminal, constant (C_L) portion of the light polypeptide chain. Two types of neutral proteases, designated elastase-like (ELP) and chymotrypsin-like (CLP), have been isolated and purified from human polymorphonuclear leukocytes. Because these proteases have defined proteolytic activity under physiologic conditions for several types of human proteins, we investigated their effect on human Bence Jones proteins. Incubation of -type or -type Bence Jones proteins with ELP or CLP under appropriate conditions resulted in cleavage of both types of light chains as evident by immunochemical and electrophoretic analyses. Treatment with ELP or CLP of one Bence Jones protein resulted in the formation of a single component that had antigenic and electrophoretic properties similar to the V_L fragment derived from pepsin digestion of the native protein. No component corresponding to the C_L could be detected immunochemically or electrophoretically. Studies of isolated pepsin-labile (37°C) and pepsin-stable (55°C) C_L fragments demonstrated the marked susceptibility of the carboxyl-terminal half of the light chain to proteolysis by the leukocyte-derived neutral proteases. Incubation with ELP of three other Bence Jones proteins and three reduced-alkylated Bence Jones proteins resulted, in each case, in the formation of a homogeneous component which was electrophoretically and immunochemically distinct from the pepsin-derived V_L fragment. An identical component could also be formed by incubating a pepsin-derived V_L fragment with ELP. In the ELP-treated samples, no C_L-related material was detected electrophoretically or immunochemically with antisera possessing specificity for C_L antigenic determinants present on the unfolded light polypeptide chain or on the isolated C_L. The component formed by ELP or CLP treatment of certain Bence Jones proteins thus appears to be V_L-related, but lacks the idiotypic antigenic determinant present on the native protein. In this respect, these neutral protease-derived light chain components are similar to the amyloid-like V_L fragments generated in vitro from certain endopeptidase-treated Bence Jones proteins.

Footnotes

¹ This work was supported in part by United States Public Health Service Research Grants CA 10056-11 and CA 15173-02 from the National Cancer Institute.

² A preliminary account of this work was presented at the annual meeting of the American Society of Hematology, Dallas, Texas, December 8, 1975.

³ Address reprint requests to: Dr. Alan Solomon, University of Tennessee Memorial Research Center, 1924 Alcoa Highway, Knoxville, Tennessee 37920.

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