Interactions of sulfite and manganous ion with peroxidase oxidation products of indole-3-acetic acid

Abstract

Chemical and spectral data were used to study the fate of IAA during the first minute of its peroxidase catalysed oxidation. In the first 30 sec of the reaction, a hypsochromic shift of 2 nm was detected in the UV spectrum of IAA. In the presence of sulfite, the rate of spectral shift is enhanced. As the oxidation of IAA proceeds, the effect of sulfite diminishes, being ineffective when added to the reaction after 20–30 sec. The loss of the sulfite effect coincides with a hyperchromic shift at 264 nm. This is not observed when sulfite is added at the beginning of the oxidation reaction. The rate of the hypochromic shift at 282 nm is greatly enhanced when sulfite is added at the start of the reaction, but is ineffective when added after 30–40 sec. The initial effect of sulfite is attributed to a chain reaction of unstable IAA-free radicals and sulfite oxidation, and this is further enhanced by manganous ions, which function in electron transfer between sulfite ions and IAA-free radicals.