Physicochemical characterization of mouse myeloma proteins revealed the individuality of each myeloma protein. When the myeloma proteins are considered collectively a wide range of individual properties were represented, including electrophoretic mobilities varying from the gamma to alpha region, hexose contents from 1 to 4 per cent, and ultracentrifugal components from 6.5 to 13 S. The 20 myeloma proteins could be divided into groups, the gamma type and the beta type myeloma globulins, on the basis of physicochemical, as well as immunoelectrophoretic, studies. Two gamma type myeloma proteins (5563, MPC-11) resembled normal gamma globulins, sedimenting as a single 6.5 S peak in the ultracentrifuge, and having a relatively low hexose content (1 per cent).

Eighteen beta type mouse myeloma proteins differed from gamma myeloma proteins and, typically, were found on ultracentrifugal analysis to have multiple components with sedimentation coefficients of 6.5, 9, 11, and 13 S, having a higher hexose content (2 to 4 per cent) as well as distinctive chromatographic and starch gel electrophoretic properties.

All of the mouse myeloma proteins were heterogeneous and heterogeneity of two types was observed. Polymer formation was responsible for the 9, 11, and/or 13 S components seen on ultracentrifugation of the beta type myeloma proteins. Starch gel electrophoresis revealed this type of heterogeneity as relatively widely separated myeloma protein components, presumably owing to the retardation effect of starch gel on the electrophoretic migration of the larger polymers. Starch gel electrophoresis revealed a different type of heterogeneity for the two gamma type myeloma proteins, each of these being shown to contain 5 or more components differing only in electrophoretic properties.

The physicochemical characteristics of the γ-type and ß-type myeloma proteins in the mouse indicated the close similarity of these proteins to the γ- and ß-2A-myeloma proteins in man.

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