title: Thiocalsin:  a thioredoxin-linked, substrate-specific protease dependent on calcium.
abstract: We describe a protease, named "thiocalsin," that is activated by  calcium but only after reductive activation by thioredoxin, a small protein with a redox-active disulfide group that functions widely in regulation.  Thiocalsin appeared to be a 14-kDa serine protease that functions independently of calmodulin.  The enzyme, purified from germinating wheat grain, specifically cleaved the major indigenous storage proteins, gliadins and glutenins, after they too had been reduced, preferentially by thioredoxin.  The disulfide groups of the enzyme, as well as its protein substrates, were reduced by thioredoxin via NADPH and the associated enzyme, NADP-thioredoxin reductase.  The results broaden the roles of thioredoxin and calcium and suggest a joint function in activating thiocalsin, thereby providing amino acids for germination and seedling development.
authors.affiliation: Department of Plant Biology, University of California, Berkeley 94720, USA.
authors.forename: I
authors.initials: I
authors.lastname: Besse
authors.forename: J H
authors.initials: JH
authors.lastname: Wong
authors.forename: K
authors.initials: K
authors.lastname: Kobrehel
authors.forename: B B
authors.initials: BB
authors.lastname: Buchanan
mesh_terms: D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D010450:Endopeptidases / Q000302:isolation & purification* / Q000378:metabolism / Q000502:physiology; D018525:Germination / Q000502:physiology*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000302:isolation & purification* / Q000378:metabolism / Q000502:physiology; D011480:Protease Inhibitors; D013379:Substrate Specificity; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism / Q000502:physiology; D013879:Thioredoxins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D014908:Triticum / Q000737:chemistry / Q000201:enzymology* / Q000502:physiology
chemical_list: D010940:Plant Proteins; D011480:Protease Inhibitors; D013879:Thioredoxins; D009249:NADP; D013880:Thioredoxin-Disulfide Reductase; D010450:Endopeptidases; D002118:Calcium