Date of Award
Doctor of Philosophy
Peroxidase (E.C.188.8.131.52) has been widely used as a marker of altered growth and development in plants. However, a definitive role of physiological significance has yet to be ascribed. This may be partially due to studies, that have been performed with a peroxidase molecule neither isolated to purity nor characterized from the system of investigation. A cationic peroxidase molecule (molecular weight 40 kD) had been purified to apparent homogenity and characterized from cultured peanut cells. Antibodies were raised against this peroxidase molecule in rabbits and used for monitoring biosynthetic studies on this peroxidase molecule in cultured peanut cells.;The cationic peroxidase constituted one sixth of the total proteins in the medium of cultured peanut cells. Peanut plant leaves also secreted the same peroxidase in to their intercellular spaces as determined by immunodiffusion assays. Cultured peanut cells synthesized ten fold more peroxidase than the peanut leaves.;By using the technique of differential centrifugation to isolate cell organelles in conjunction with immunoprecipitation it was shown that most of the newly synthesized peroxidase was found to be associated with the microsomal fraction. This peroxidase from the microsomal fraction was only released when microsomes were treated with high salt buffer (phosphate buffer with 0.8 M KCl). This indicated that the intracellular origin of the high ionic extract of peroxidase was from the microsomal pellet. Most of the newly synthesized peroxidase was associated with membrane bound polysomes, as determined by immunoprecipitation of polysomes, by using immunoaffinity purified IgGs against cationic peroxidase.;The heme moiety of peroxidase, was shown to be synthesized from glutamic acid and not from glycine and succinyl CoA, as is the case in animals. The heme moiety was identified as protoheme, based on mass spectrometry, and was synthesized in the mitochondria of cultured peanut cells. The heme was present in equimolar concentration to apoprotein and was found to be essential for peroxidative as well as IAA-oxidase activities of this peroxidase molecule.;No appreciable differences in the enzymatic activities associated with peroxidase could be detected between the purified cationic and anionic peroxidases from cultured peanut cells. Nevertheless, cationic form of peroxidase was the major isozyme that was secreted by cultured peanut cells. The significance of the secretion of the cationic form in relation to its mode of action was discussed.
Chibbar, Ravindra Nath, "Biosynthesis Of Peroxidase In Peanut Cells In Suspension Culture" (1984). Digitized Theses. 1367.