Many cases of lactate dehydrogenase (LDH) linked immunoglobulins have been previously reported. These complexes were of great interest in connection with autoimmune diseases, but it has not been clear whether these LDH linked immunoglobulins were specific antigen-antibody complexes or nonimmunological protein-protein bindings.
In this report, the properties of nineteen cases of LDH linked immunoglobulins (eight cases of complexes with IgG and eleven of IgA) were studied.
The type of light chain were determined to be exclusively κ type irrespective of heavy chain class.
Apparent Michaelis constant, K_m, for lactate of these complex-forming and normal LDH was determined to be identical by double reciprocal analysis. Thus, it was proved that the active site of lactate dehydrogenase was not interfered by the complex-formation with immunoglobulins.
Papain digestion of these LDH linked immunoglobulins was carried out to investigate the binding mode of these complexes. Immunoelectrophoresis followed by LDH activity staining was carried out for the digested immunoglobulins using specific antibody for Fc, Fab, and light chains. The precipitin lines against Fab and κ light chain were proved to have LDH activity, but that against Fc was not. The molecular size of these digested complexes were determined to be smaller by thin layer gel-filtration using Sephadex G-200 superfine. It was elucidated that the binding site of these LDH linked immunoglobulins was located in Fab portions. And this fact indicates that these complexes are formed by specific antigen-antibody bindings.
Thus the complex forming immunoglobulins must be recognized as one of the circulating autoantibodies.

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The total activity of lactate dehydrogenese (LDH) and LDH isozyme patterns were investigated in adult female rabbit genital organs before and after implantation. The animals were divided into four groups, namely follicular, ovulation, pre-implantation and implantation stage group. The results obtained are as follows.
1. The LDH activity in Fallopian tube, uterus and ovary was lowest in follicular and implantation stage group, and higher in ovulation stage group and highest in pre-implantation stage group.
2. The LDH activity in plasma, on the contrary, showed minimum value in pre-implantation stage group.
3. The LDH activity of pre-implantation stage was three times as high as that of ovulation stage group in Fallopian tube and uterus.
4. The LDH activity of Fallopian tube was twice as high as that of uterus in all four groups.
5. LDH isozyme analysis by agar electrophoresis revealed that the LDH isozyme pattern in Fallopian tube was LDH₅ type and LDH isozyme pattern in uterus was LDH₁ type.
6. There were no definite differences in LDH isozyme patterns among four groups.
7. The LDH isozyme pattern in plasma showed LDH₁ type in follicular and pre-implantation stage group, and LDH₅ type in ovulation and implantation stage group.

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Low molecular proteins contained in the urine of the patients of multiple myeloma and diabetes mellitus were studied physicochemically and immunologically. Urinary low molecular proteins, approximately 10, 000 to 50, 000 in molecular weight, were concentrated about 100 times by ultrafiltration.
Immunoelectrophoresis of these low molecular proteins revealed fractions common in antigenic properties with albumin, α₁-antitrypsin, ceruloplasmin, transferrin, IgG and Bence-Jones protein. The low molecular weight albumin was separated and purified by chromatography on Sephadex G-75 and DEAE-cellulose. Purity of this albumin was checked by double immunodiffusion and polyacrylamide gel disc electrophoresis. The approximate molecular weight of this albumin was measured as 10, 000 by ultracentrifugal and light scattering analysis. The ability of the low molecular fraction to induce formation of antibody was confirmed with experimental inoculation to rabbits.

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