Turnover of Catalase Heme and Apoprotein Moieties in Cotyledons of Sunflower Seedlings

Abstract

The turnover of catalase apoprotein and catalase heme was studied in cotyledons of sunflower (Helianthus annuus L.) seedlings by density labeling of apoprotein and radioactive labeling of heme moieties. The heavy isotope (50% 2H20) and the radioactive isotope ([14C]5-aminolevulinic acid) were applied either during growth in the dark (day 0-2.5) or in the light (day 2.5 and 5). Following isopycnic centrifugation of catalase purified from cotyledons of 5-day-old seedlings, superimposition curve fitting was used to determine the amounts of radioactive heme moieties in native and density-labeled catalase. Data from these determinations indicated that turnover of catalase heme and apoprotein essentially was coordinate. Only small amounts of heme groups were recycled into newly synthesized apoprotein during growth in the light, and no evidence was found for an exchange of heme groups in apoprotein moieties. It followed from these observations that degradation of catalase apoprotein was slightly faster than that of catalase heme. A degradation constant for catalase apoprotein of 0.263 per day was determined from the data on heme recycling and the degradation constant of catalase heme determined previously to be 0.205 per day (R Eising, B Gerhardt [1987] Plant Physiol 84: 225-232).In comparison with the increment of our knowledge on the biogenesis of peroxisomal proteins in plants in the last several years, only little progress was made in understanding the turnover (degradation) of proteins from plant peroxisomes. Results obtained from a few studies indicate that the general mechanism is one of individual protein degradation rather than a degradation of the whole organelles (1,8,9,11,12,22,27,28). The concept of individual protein degradation suggests that (at least) initiating steps of the degradative pathway are localized in the peroxisomes. These steps are not necessarily proteolytic processes, but could be any chemical modification (e.g. oxidation, dephosphorylation), or a specific export of proteins destined for degradation in other cell compartments.

Vitiligo: A Possible Model of Degenerative Diseases

“…1D) could explain the persistent stimulation of antioxidant and detoxification genes in vitiligo melanocytes, whereas attenuated protein expression could be directly caused by altered intracellular redox balance affecting enzymes stability. In fact, it has been demonstrated that acceleration of catalase degradation caused by H 2 O 2 determines the increase of the corresponding gene transcription, producing a constant stady-state level of protein expression [27]. Activation of antioxidant gene expression indicated a compromised redox homeostasis in melanocytes isolated from vitiligo patients.…”

Novel insights in mammalian catalase heme maturation: Effect of NO and thioredoxin-1

“…This interaction is also shown to inhibit catalase tetramerization, suggesting tetramerization of catalase is a peroxisomal event(45,48). However, several other reports suggest that cytosolic assembly of catalase can occur independent of peroxisomes (15,49,50). Four amino acids on the N-terminal end of Candida Tropicalis catalase are shown to regulate tetramerization of the protein(51).…”

“…In rat liver apo-catalase is present in 3 fold excess (1.6% compared to 0.5%) of holo-monomeric catalase (13). Lack of heme can increase the pool of apo-catalase and may promote its turnover (14,15). Exposure to oxidative stress can inactivate catalase (16-19), but whether this affects its structure is not completely understood.…”