title: Calorimetric investigation of protein/amino acid interactions in the solid state.
abstract: Possible protein/amino acid interactions and the physical states of amino acids after freeze-drying have been studied using isoperibol calorimetry and differential scanning calorimetry (DSC). Good linear correlations (R(2) = 0.99) between the enthalpies of solution and the percentage of antibody in all physical mixtures, as well as unchanging melting temperatures of amino acids for physical mixtures demonstrated that there is no interaction between the antibodies and amino acids studied upon physical mixing. On the other hand, positive deviations for antibody/histidine and antibody/arginine freeze-dried samples obtained from the isoperibol calorimetry results demonstrated that molecular level interactions, such as ion-dipole or electrostatic interactions or hydrogen bonding, occur between antibodies and histidine or arginine. The values of DeltaH(interaction) for antibody/histidine (1:1, w/w) and antibody/arginine (1:1, w/w) lyophilized samples were approximately 8 kJ/mol. These interactions were also confirmed by decreased and/or the disappearance of melting temperatures of the amino acids with DSC measurements. A negative deviation from linearity was detected for antibody/aspartic acid lyophilized samples which indicated partial amorphization of aspartic acid. No deviation from linearity as well as similar melting temperatures of antibody/glycine lyophilized samples indicated the absence of interactions between the antibodies and glycine upon freeze-drying.
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, 2095 Constant Avenue, Lawrence, KS 66047, USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Tian
authors.forename: Samir
authors.initials: S
authors.lastname: Sane
authors.forename: J Howard
authors.initials: JH
authors.lastname: Rytting
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D000906:Antibodies / Q000737:chemistry; D001120:Arginine / Q000737:chemistry; D001224:Aspartic Acid / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D003850:Deoxyribonuclease I / Q000737:chemistry / Q000235:genetics; D004795:Enzyme Stability; D005612:Freeze Drying; D006639:Histidine / Q000737:chemistry; D011489:Protein Denaturation; D011506:Proteins / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D012996:Solutions; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D000906:Antibodies; D011506:Proteins; D011994:Recombinant Proteins; D012996:Solutions; D001224:Aspartic Acid; D006639:Histidine; D001120:Arginine; D003850:Deoxyribonuclease I