Optical rotatory dispersion and the conformation of human gamma-globulin

Heterogeneity of Monoclonal Antibodies

Heterogeneity of monoclonal antibodies is common due to the various modifications introduced over the lifespan of the molecules from the point of synthesis to the point of complete clearance from the subjects. The vast number of modifications presents great challenge to the thorough characterization of the molecules. This article reviews the current knowledge of enzymatic and nonenzymatic modifications of monoclonal antibodies including the common ones such as incomplete disulfide bond formation, glycosylation, N-terminal pyroglutamine cyclization, C-terminal lysine processing, deamidation, isomerization, and oxidation, and less common ones such as modification of the N-terminal amino acids by maleuric acid and amidation of the C-terminal amino acid. In addition, noncovalent associations with other molecules, conformational diversity and aggregation of monoclonal antibodies are also discussed. Through a complete understanding of the heterogeneity of monoclonal antibodies, strategies can be employed to better identify the potential modifications and thoroughly characterize the molecules.

ORGAN SPECIFICITY AND LACTATE-DEHYDROGENASE ACTIVITY. DIFFERENTIAL INHIBITION BY UREA AND RELATED COMPOUNDS

1. The effect of urea on the lactate-dehydrogenase activities of human-heart and -liver tissue extracts and on crystalline ox-heart and rabbit-muscle enzyme have been determined. Similar studies on electrophoretically separated isoenzyme fractions have shown an inverse relationship between sensitivity to urea inhibition and electrophoretic mobility. 2. With pyruvate as substrate a sharp change in the nature of the inhibition of tissue lactate dehydrogenase with increasing concentrations of urea occurs at 1 m or 4 m with the electrophoretically slow and fast isoenzymes respectively. 3. At concentrations of urea less than 1 m, inhibition of the purified enzymes is competitive with respect to pyruvate and 2-oxobutyrate. 4. Similar studies have been carried out with methylurea and hydantoic acid, both of which are more potent inhibitors than urea.

Structural properties of the myelin-associated glycoprotein ectodomain

Myelin-associated glycoprotein (MAG) has been proposed to mediate adhesive interactions during myelin development. We have used the baculovirus expression system to produce a truncated form of this molecule [soluble extracellular domain of MAG (sMAG)] consisting of the complete extracellular ectodomain. Spectroscopic studies indicate a high beta-sheet content, consistent with the prediction of Ig-like structure. Hydrodynamic studies indicate an asymmetric monomer, with a Stokes radius of 4.1-4.6 nm, a sedimentation coefficient of 3.6S, and a frictional ratio of approximately 1.6. We postulate that the outer two Ig-like domains form a unit that folds back over the rest of the molecule. Fluorescence quenching studies indicate that sMAG interacts with divalent cations and may have a functional lectin domain.

Laser Raman investigation of the conformation of human immunoglobulin G

Laser Raman spectra of human immunoglobulin G in neutral solution, as well as in the lyophilized and alkaline-denatured states are presented. In the spectrum of the native protein, the amide III band appears at 1240 cm-1 and is assigned to the presence of beta-sheet structure. From its intensity, using a procedure described in this paper, we evaluate the beta-structure content to 37 +/- 4%. This result is supported by the strong amide I' band at 1667 cm-1 and by the presence in the spectra of two bands at 991 and 1078 cm-1, respectively assigned to the C-C and C-N skeletal stretching modes. The differences between the spectrum of the lyophilized powder and that of the solution show that the lyophilization process induces conformational changes that perturb the local environment of some of the tryptophan residues and alter the secondary structure of immunoglobulin G. The beta-structure appears to be more uniform and more abundant in solution. When the protein is denatured at pH 11, the amide III and amide I'bands, which become weaker and broader, shift in frequency from 1240 to 1248 cm-1 and from 1667 to 1656 cm-1 respectively. These changes indicate a decrease in the amount of beta-structure and a transition toward a much more disordered conformation. During the denaturation, the intensities of many bands of the aromatic chromophores change, notably the tryptophan peaks at 879, 1359 and 1573 cm-1.