Structural studies on human serum gamma‐globulins and myeloma proteins. I. Fragmentation and denaturation of the globulins with detergent and alkali.

The denaturation of human serum γ‐globulin and myeloma protein was studied by sedimentation, viscosity, and optical rotatory dispersion methods. Sodium decyl sulfate, in alkaline solutions of p H 10.2–11.0, was found to be very effective at sufficiently high concentrations of the detergent and higher temperatures of 50°C. The macromolecules of the globulins were inflated (or unfolded) and split into fragments having molecular weight of approximately 60,000. The optical activity measurements showed that the b 0 values of the native globulins were near zero, and that they became negative on denaturation and fragmentation. The levorotation thereby increased. Upon removal of the detergent by dialysis the b 0 returned to zero, while the levorotation remained strongly negative. The fragments thereby tended to aggregate, especially when the p H was decreased to near neutrality. It was concluded that the structural changes occurred in the following steps: (1) Native, ordered macromolecule → (2) Disorganized and fragmented macromolecule → (3) Partially organized fragments → (4) Strongly disorganized and aggregated fragments. A tentative schematic model of the globulin macromolecule was presented in which a non‐helical order is assumed in the native state, and the detergent‐alkali fragmentation and denaturation explained as chain separation and further conformational transition of the separated subunits.