ABSTRACT
A recent study reports discordant results for maximal free-radical yields from the decomposition of peroxynitrous acid using different assay reagents and a puzzling decrease (to zero) of the radical yields with increasing pH. An assay method using 2,2,'azino-bis(3-ethyl-benzthiazoline sulphonate) (ABTS) has been tested using stopped-flow kinetic studies, and the results imply that the assay is satisfactory when [HOONO] much greater than [-OONO] but that reactions involving peroxynitrite anion interfere at higher pH. Evidence is presented that peroxynitrite was an interfering species in the earlier studies.
Subject(s)
Nitrates/chemistry , Benzothiazoles , Free Radicals , Hydrogen-Ion Concentration , Indicators and Reagents , Kinetics , Nitric Oxide/chemistry , Sulfonic Acids , Superoxides/chemistryABSTRACT
Tyrosine markedly attenuates the chemiluminescence output intensity from the 4-iodophenol enhanced chemiluminescence assay system in a manner consistent with competition between the amino acid and luminol for the 4-iodophenoxy radical. This effect provides the basis for a sensitive assay of tyrosine. Interference by the other amino acids has been assessed; major interference by cysteine can be removed by incubation with iodoacetic acid.
Subject(s)
Iodobenzenes/pharmacology , Luminescent Measurements , Tyrosine/analysis , Chloromercuribenzoates , Iodoacetates , Iodoacetic Acid , Iodobenzenes/chemistry , Sensitivity and Specificity , Sulfhydryl Compounds , p-Chloromercuribenzoic AcidABSTRACT
The intensity of 4-I-phenol-enhanced chemiluminescence from the luminol-H2O2-horseradish peroxidase system is markedly attenuated in the presence of low concentrations of non-enhancer phenols. Under the conditions studied, the effect is not associated with competition between 4-I-phenol and non-enhancer phenol for the enzyme intermediates, Compounds I and II, but involves a competition between non-enhancer phenol and luminol most probably for the 4-I-phenoxy radical.
