title: A comparative reactivity study of microperoxidases based on hemin, mesohemin and deuterohemin.
abstract: Three microperoxidases--hemin-6(7)-gly-gly-his methyl ester (HGGH), mesohemin-6(7)-gly-gly-his methyl ester (MGGH) and deuterohemin-6(7)-gly-gly-his methyl ester (DGGH)--have been prepared as models for heme-containing peroxidases by condensation of glycyl-glycyl-L-histidine methyl ester with the propionic side chains of hemin, mesohemin and deuterohemin, respectively. The three microperoxidases differ in two substituents, R, of the protoporphyrin IX framework (HGGH: R=vinyl, MGGH: R=ethyl, DGGH: R=H). X-band and high field EPR spectra show that the microperoxidases exhibit spectroscopic properties similar to those of metmyoglobin, i.e. a high spin ferric S=5/2 signal at g(perpendicular)=6 and g parallel)=2 and an estimated D value of 7.5+/-1cm(-1). The catalytic activities of the microperoxidases towards K4[Fe(CN)6], L-tyrosine methyl ester and 2,2'-azino(bis(3-ethylbenzothiazoline-6-sulfonic acid)) (ABTS) have been investigated. It was found that all three microperoxidases exhibit peroxidase activity and that the reactions follow the generally accepted peroxidase reaction scheme [Biochem. J. 145 (1975) 93-103] with the exception that the initial formation of a Compound I analogue is the rate-limiting step for the whole process. The general activity trend was found to be MGGH approximately DGGH>HGGH. For each microperoxidase, DFT calculations (B3LYP) were made on the reactions of compounds 0, I and II with H+, e- and H+ + e-, respectively, in order to probe the possible relationship between the nature of the 2- and 4-substituents of the hemin and the observed reactivity. The computational modeling indicates that the relative energy differences are very small; solvation and electrostatic effects may be factors that decide the relative activities of the microperoxidases.
authors.affiliation: Inorganic Chemistry, Center for Chemistry and Chemical Engineering, Lund University, Box 124, SE-221 00 Lund, Sweden.
authors.forename: Ekaterina S
authors.initials: ES
authors.lastname: Ryabova
authors.forename: Patrik
authors.initials: P
authors.lastname: Rydberg
authors.forename: Matthias
authors.initials: M
authors.lastname: Kolberg
authors.forename: Espen
authors.initials: E
authors.lastname: Harbitz
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Barra
authors.forename: Ulf
authors.initials: U
authors.lastname: Ryde
authors.forename: K Kristoffer
authors.initials: KK
authors.lastname: Andersson
authors.forename: Ebbe
authors.initials: E
authors.lastname: Nordlander
mesh_terms: D052160:Benzothiazoles; D019295:Computational Biology; D004151:Dipeptides / Q000737:chemistry; D004563:Electrochemistry; D006418:Heme / Q000378:metabolism*; D006427:Hemin / Q000031:analogs & derivatives* / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008652:Mesoporphyrins / Q000378:metabolism*; D008954:Models, Biological; D009842:Oligopeptides / Q000138:chemical synthesis; D010544:Peroxidases / Q000378:metabolism*; D013451:Sulfonic Acids / Q000737:chemistry; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D052160:Benzothiazoles; D004151:Dipeptides; D008652:Mesoporphyrins; D009842:Oligopeptides; D013451:Sulfonic Acids; C040444:tyrosine methyl ester; C011219:deuterohemin; C027787:glycylhistidine; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; D014443:Tyrosine; D006418:Heme; C031468:mesoporphyrin IX; D006427:Hemin; D006861:Hydrogen Peroxide; D010544:Peroxidases; C021799:microperoxidase