Biomaterial Database

pH dependence of the active site of horseradish peroxidase compound II. 1993

C S Chang, and I Yamazaki, and R Sinclair, and S Khalid, and L Powers

National Center for the Design of Molecular Function, Utah State University, Logan 84322-4630.

Using X-ray absorption spectroscopy, we investigated the active site of horseradish peroxidase (HRP) compound II at two different pH values. The results indicate that the bond length of the sixth coordinated ligand of the active site was 1.90 +/- 0.02 A at pH 7, decreasing to 1.72 +/- 0.02 A at pH 10. The average iron-to-pyrrole nitrogen and the proximal ligand bond lengths showed no significant changes. The position of higher coordination shells around the iron center changed, implying that some movement or deformation of nearby amino acid residues and/or of the heme occurred. Results of this study suggest that the decrease of the Fe-O bond length of HRP compound II at the higher pH might be attributed to the loss of a hydrogen bond which is present between the oxygen ligand and an amino acid residue in the heme pocket at pH 7.

UI	MeSH Term	Description	Entries
D007501	Iron	A metallic element with atomic symbol Fe, atomic number 26, and atomic weight 55.85. It is an essential constituent of HEMOGLOBINS; CYTOCHROMES; and IRON-BINDING PROTEINS. It plays a role in cellular redox reactions and in the transport of OXYGEN.	Iron-56,Iron 56
D007527	Isoenzymes	Structurally related forms of an enzyme. Each isoenzyme has the same mechanism and classification, but differs in its chemical, physical, or immunological characteristics.	Alloenzyme,Allozyme,Isoenzyme,Isozyme,Isozymes,Alloenzymes,Allozymes
D008024	Ligands	A molecule that binds to another molecule, used especially to refer to a small molecule that binds specifically to a larger molecule, e.g., an antigen binding to an antibody, a hormone or neurotransmitter binding to a receptor, or a substrate or allosteric effector binding to an enzyme. Ligands are also molecules that donate or accept a pair of electrons to form a coordinate covalent bond with the central metal atom of a coordination complex. (From Dorland, 27th ed)	Ligand
D008958	Models, Molecular	Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.	Molecular Models,Model, Molecular,Molecular Model
D011487	Protein Conformation	The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).	Conformation, Protein,Conformations, Protein,Protein Conformations
D011758	Pyrroles	Azoles of one NITROGEN and two double bonds that have aromatic chemical properties.	Pyrrole
D006735	Horseradish Peroxidase	An enzyme isolated from horseradish which is able to act as an antigen. It is frequently used as a histochemical tracer for light and electron microscopy. Its antigenicity has permitted its use as a combined antigen and marker in experimental immunology.	Alpha-Peroxidase,Ferrihorseradish Peroxidase,Horseradish Peroxidase II,Horseradish Peroxidase III,Alpha Peroxidase,II, Horseradish Peroxidase,III, Horseradish Peroxidase,Peroxidase II, Horseradish,Peroxidase III, Horseradish,Peroxidase, Ferrihorseradish,Peroxidase, Horseradish
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D015502	Absorptiometry, Photon	A noninvasive method for assessing BODY COMPOSITION. It is based on the differential absorption of X-RAYS (or GAMMA RAYS) by different tissues such as bone, fat and other soft tissues. The source of (X-ray or gamma-ray) photon beam is generated either from radioisotopes such as GADOLINIUM 153, IODINE 125, or Americanium 241 which emit GAMMA RAYS in the appropriate range; or from an X-ray tube which produces X-RAYS in the desired range. It is primarily used for quantitating BONE MINERAL CONTENT, especially for the diagnosis of OSTEOPOROSIS, and also in measuring BONE MINERALIZATION.	Absorptiometry, X-Ray,Dual-Photon Absorptiometry,Photodensitometry, X-Ray,Photon Absorptiometry,Single-Photon Absorptiometry,X-Ray Absorptiometry,Absorptiometry, Dual X-Ray,Absorptiometry, Dual-Energy Radiographic,Absorptiometry, Dual-Energy X-Ray,DEXA Scan,DPX Absorptiometry,DXA Scan,Densitometry, X-Ray,Densitometry, Xray,Dual X-Ray Absorptiometry,Dual-Energy Radiographic Absorptiometry,Dual-Energy X-Ray Absorptiometry,Dual-Energy X-Ray Absorptiometry Scan,Radiographic Absorptiometry, Dual-Energy,X-Ray Absorptiometry, Dual-Energy,X-Ray Photodensitometry,Absorptiometries, DPX,Absorptiometry, DPX,Absorptiometry, Dual Energy Radiographic,Absorptiometry, Dual Energy X Ray,Absorptiometry, Dual X Ray,Absorptiometry, Dual-Photon,Absorptiometry, Single-Photon,Absorptiometry, X Ray,DEXA Scans,DXA Scans,Densitometry, X Ray,Dual Energy Radiographic Absorptiometry,Dual Energy X Ray Absorptiometry,Dual Energy X Ray Absorptiometry Scan,Dual Photon Absorptiometry,Dual X Ray Absorptiometry,Photodensitometry, X Ray,Radiographic Absorptiometry, Dual Energy,Scan, DEXA,Scan, DXA,Scans, DEXA,Scans, DXA,Single Photon Absorptiometry,X Ray Absorptiometry,X Ray Absorptiometry, Dual Energy,X Ray Photodensitometry,X-Ray Absorptiometry, Dual,X-Ray Densitometry,Xray Densitometry