Abstract
Combined optical and conductimetric measurements in aqueous solution indicate that at high pH (greater than or equal to 10).OH radicals react with the phenoxide form of 2,4-dihydroxybenzoic acid to form transiently phenoxyl radicals and a small amount of hydroxyeyclohexadienyl (HCHD) radicals by 150 ns. The respective yields of 88 and 12% of the total.OH radical yield were deduced from conductance and optical changes as well as from studies using a low potential reductant. The HCHD radical possesses a pKa of 8.0 +/- 0.1 and the constructed spectrum of the deprotonated forms of HCHD has a lambda max at 420 nm with a minimum extinction coefficient of approximately 7250 M-1 cm-1. The red shift in lambda max and increase in extinction coefficient compared to the revised spectral properties of the protonated form of the HCHD radical (lambda max at 390 nm with extinction coefficient of approximately 4500 M-1 cm-1), together with the pKa of the HCHD radical, provide an explanation for the pH-dependent spectral changes of the so-called highly absorbing intermediate II species, observed in the functioning of the enzyme p-hydroxybenzoate hydroxylase. These results add further to the evidence in support of the proposal that intermediate II is composed of species which absorb similarly to the flavin 4(a)-hydroxide and a form of the substrate/product such as the HCHD radical (Anderson, R. F., Patel, K. B., and Stratford, M. R. L. (1987) J. Biol. Chem. 262, 17475-17479).
Highlights
From the Grav Laboratorv of the Cancer Research Camnaign, Post Office Box 100, Mount Vernon Hospital, Northwood, Middlesex, HA6 ZJR, United Kingdom
-4500 M" cm"), together with the pK, of the HCHD In this studywe extend ourprevious work on 2,4-dihydroxradical, provide an explanation for the pH-dependent ybenzoic acid (8) to the high pH region to see if the radical spectral changes of the so-called highly absorbing in- chemistry of this substrate can account for the distinctive termediate I1 species, observed in the functioning of spectral changes in its respective intermediate I1 species
Reactions initiated by the 'OH radical are conveniently studied in irradiated aqueous solution saturated with N 2 0gas to convert (e,) into 'OH radicals as follows
Summary
From the Grav Laboratorv of the Cancer Research Camnaign, Post Office Box 100, Mount Vernon Hospital, Northwood, Middlesex, HA6 ZJR, United Kingdom. The red shift in X, and increase in extinction coefficient compared to the revised spectral properties of the protonated form of the HCHD radical (X, at 390 nm with extinction coefficient of for both p-hydroxybenzoate hydroxylase (8), and phenol hydroxylase (9), with a flavin 4(a)-substituted species (such as the flavin 4(a)-hydroxide, intermediate 111). -4500 M" cm"), together with the pK, of the HCHD In this studywe extend ourprevious work on 2,4-dihydroxradical, provide an explanation for the pH-dependent ybenzoic acid (8) to the high pH region to see if the radical spectral changes of the so-called highly absorbing in- chemistry of this substrate can account for the distinctive termediate I1 species, observed in the functioning of spectral changes in its respective intermediate I1 species. The risetime of the complete detection electronics was
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
