A comparative kinetic study on the singlet molecular oxygen-mediated photoxidation of alpha- and beta-chymotrypsins.
Kinetic aspects of the sensitized photooxidation of alpha- and beta-chymotrypsins have been studied at pH 6 and 8. The sensitization, employing classical O2(1Deltag)-photogenerators, such as xanthene dyes, is a kinetically intricate process because of the presence of ground state dye-protein associations and to the simultaneous participation of superoxide ion and singlet molecular oxygen [O2(1Deltag)]. Both proteins, that possess the same distribution pattern of photooxidizable amino acids, suffer a pure O2(1Deltag)-mediated photodynamic attack, using the carbonylic sensitizer Perinaphthenone. Overall and reactive rate constants for the O2(1Deltag)-quenching (in the order of 108 and 107/M/s, respectively), and rates of oxygen consumption determined by time-resolved, spectroscopic and polarographic methods indicate that alpha- and beta-chymotrypsins are less photooxidizable at pH 6, as a result of an enhancement of the O2(1Deltag)-physical quenching component. In general terms, beta-chymotrypsin exhibits the greater overall proclivity to interact with O2(1Deltag), whereas structural factors, possibly evidenced by a higher exposure of the reactive tryptophan residues, impart an increased photooxidation degree to the proteins at pH 8, specially to the alpha-chymotrypsin.
Biasutti
M A
MA
Dpto. de Química, Universidad Nacional de Río Cuarto, 5800-Río Cuarto, Argentina. abiasutti@exa.unrc.edu.ar
Posadaz
A
A
García
N A
NA
D002918:Chymotrypsin / Q000737:chemistry*; D004801:Eosine Yellowish-(YS) / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D043803:Phenalenes / Q000737:chemistry; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000737:chemistry; D012395:Rose Bengal / Q000737:chemistry; D026082:Singlet Oxygen / Q000737:chemistry*
D005456:Fluorescent Dyes; D043803:Phenalenes; D017319:Photosensitizing Agents; D026082:Singlet Oxygen; D012395:Rose Bengal; C038036:phenalen-1-one; D002918:Chymotrypsin; D004801:Eosine Yellowish-(YS)