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PLANT PHYSIOLOGY , Vol 114, Issue 2 715-722, Copyright © 1997 by American Society of Plant Biologists

BIOCHEMISTRY AND ENZYMOLOGY

A Plant Chloroplast Glutamyl Proteinase

W. A. Laing and J. T. Christeller
HortResearch, Private Bag 92169, Auckland, New Zealand (W.A.L.)

A glutamyl proteinase was partially purified from Percoll gradient-purified spinach (Spinacia oleracea) chloroplast preparations and appeared to be predominantly localized in the chloroplast stroma. The enzyme degraded casein, but of the 11 synthetic endopeptidase substrates tested, only benzyloxycarbonyl-leucine-leucine-glutamic acid-[beta]-napthylamide was hydrolyzed at measurable rates. In addition, the enzyme cleaved the oxidized [beta]-chain of insulin after a glutamic acid residue. There was no evidence that native ribulose-1,5-bisphosphate carboxylase/oxygenase was cleaved by this proteinase. The apparent Km for benzyloxycarbonyl-leucine-leucine-glutamic acid-[beta]NA at the pH optimum of 8.0 was about 1 mM. Cl-ions were required for both activity and stability. Of the proteinase inhibitors covering all four classes of the endopeptidases, only 4-(2-aminoethyl)-benzenesulfonyl-fluoride HCl and L-1-chloro-3-[4-tosylamido]-4-phenyl-2-butanone significantly inhibited the proteinase. The partially purified enzyme had a molecular weight of about 350,000 to 380,000, based on size-exclusion chromatography. The enzyme has both similar and distinctive properties to those of the bacterial glutamyl proteinases. To our knowledge, this is the first description of a plant glutamyl proteinase found predominantly or exclusively in the chloroplast.




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Copyright © 1997 by the American Society of Plant Biologists