title: Correlation of the character of intramolecular melting with digestibility by pepsin in precipitating and non-precipitating pig anti-Dnp antibodies.
abstract: Precipitating and non-precipitating pig anti-2,4-dinitrophenyl group (Dnp) antibodies were investigated by differential adiabatic scanning microcalorimetry in the pH range 3.7-4.5. The partial heat capacity functions obtained revealed a notable difference between the two antibody types when the analysis was done at pH 4.5 or 4.0. The transition observed at temps around 50 degrees C in a non-precipitating antibody was absent in a precipitating antibody. Under analogous conditions, pH 4.5, the precipitating antibody was fully resistant to pepsin, while the non-precipitating antibody yielded appropriate F(ab')2 and pFc'fragments. At pH 3.7 no substantial difference in the partial heat capacity function could be observed between the two antibody types. Below pH 4.0 the precipitating antibody became susceptible to peptic cleavage and yielded fragments of the same general character as the non-precipitating antibody. This finding lends support to the view that the structural block in immunoglobulin G that melts first, i.e. at temps near 50 degrees C, is the CH2 domain or a part of it.
mesh_terms: D019297:2,4-Dinitrophenol; D000818:Animals; D011232:Chemical Precipitation; D004140:Dinitrophenols / Q000276:immunology*; D006863:Hydrogen-Ion Concentration; D007074:Immunoglobulin G; D010434:Pepsin A / Q000494:pharmacology; D013552:Swine / Q000276:immunology; D013696:Temperature
chemical_list: D004140:Dinitrophenols; D007074:Immunoglobulin G; D010434:Pepsin A; D019297:2,4-Dinitrophenol