Low molecular weight, heat-sensitive proteins isolated from urine of multiple myeloma patients: Caputo, Aminoacidosi 7, 163-77 (1957), C.A. 54, 6841 (1960). Used as a model in structural studies of immunoglobulins, they are structurally homogeneous within each patient and antigenically related. Crystallographic structural study: E. E. Aeola et al., Biochemistry 19, 432 (1980). They constitute the light-chain component of myeloma globulin and have been implicated in the pathogenesis of amyloidosis, cf. G. G. Glenner, N. Engl. J. Med. 302, 1283 (1980); G. G. Glenner et al., Amyloid and Amyloidosis (Excerpta Medica, Amsterdam, 1980) p 351.