Acyl Carrier Protein Is Conjugated to Glutathione in Spinach Seed

Abstract

Acyl carrier protein (ACP) contains an essential sulfhydryl group in its phosphopantetheine prosthetic group. We have investigated the state of this sulfhydryl in developing and mature spinach seed (Spinacia oleracea). Seed extracts were separated on sodium dodecyl sulfate or native polyacrylamide gels, blotted to nitrocellulose, and probed with antibodies raised against spinach ACP-I. In extracts of mature seeds prepared with reducing agents, ACP-11 migrated as a single major band, whereas extracts prepared without reducing agents gave two major bands. The additional band was identified as a conjugate of ACP-11 to glutathione (ACP-S-S-G) on the basis of its sensitivity to reducing agents and its comigration with standards in both native and sodium dodecyl sulfate gel electrophoresis. In developing spinach seeds ACP-1l exists primarily in its free sulfhydryl form or as acyl derivatives, with essentially no ACP-S-S-G present. During later stages of seed development, as seed water content declines, ACP-S-S-G accumulates to approximately 50% of the total ACP. Seed imbibition results in a rapid decline in ACP-S-S-G levels. The ACP-S-S-G:ACP-SH ratio of seeds during storage was found to be a function of seed water content and this could be manipulated by controlling the relative humidity under which the seeds were stored. We speculate that conjugation of ACP to glutathione protects the ACP from sulfhydryl oxidative damage in dry seeds.The synthesis of fatty acids in plants occurs mainly in plastids and is catalyzed by a series of enzymes together with the protein cofactor, ACP3 (6). In plants, ACP is a small (ca. 9000 D), acidic cofactor which plays a central role in plant lipid metabolism (13). A phosphopantetheine prosthetic group is attached to a seine residue near the middle of the polypeptide and is the site at which acyl chains are esterified during the reactions of fatty acid assembly. In addition to the six enzymatic steps of fatty acid synthesis, ACP also participates in reactions catalyzed by stearoyl-ACP desaturase, two acyl-ACP dependent chloroplast acyltransferases which acylate glycerol-3-phosphate and oleoyl-ACP thioesterase, which

Expression of a rice glutaredoxin in aleurone layers of developing and mature seeds: subcellular localization and possible functions in antioxidant defense

“…However, it is possible that the protein is involved in the desiccation tolerance of aleurone cells during maturation drying. During the late stage of seed development, the formation of a mixed disulfide of GSH and proteins increases in spinach and wheat seeds (Butt and Ohlrogge 1991;Rhazi et al 2003), and this situation is reversed during imbibition (Butt and Ohlrogge 1991). The glutathionylation of proteins and the formation of disulfide bonds in proteins were suggested to contribute to the desiccation tolerance of seeds by protecting Cys residues from irreversible oxidation (Colville and Kranner 2010).…”

Desiccation tolerant plants as model systems to study redox regulation of protein thiols

“…Examples for protein S-glutathionylation in seeds and desiccation tolerant plants Butt and Ohlrogge (1991) reported on S-glutathionylation of an acyl carrier protein in seeds of Spinacia oleracea during seed maturation in parallel with a decrease in the GSH/GSSG ratio and a decline in GR activity. In mature dry seeds half of the total acyl carrier protein was S-glutathionylated, and this was rapidly reversed during imbibition so that within 24 h only the reduced form of acyl carrier protein was detected.…”

Ageing-induced changes in glutathione system of sunflower seeds

“…These Free radical-induced lipid peroxidation and oxidative defence mechanisms involve several enzymatic and nonstress can damage membranes, enzymes, and nucleic ac-enzymatic antioxidants, such as the glutathione/gluids, resulting in a loss of seed viability (Smith and Ber-tathione reductase system. The imbibition capacity of preweighed seeds (Butt and Ohlrogge 1991). Upon scavenging system occurs in response to a variety of removal from the ageing conditions, the seeds were stress situations that lead to oxidative damage (Aischer dried in a drying cabinet at 30°C to the original moisture 1989, Rennenberg and Brunold 1994).…”