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Plant Physiology 85:375-378 (1987)
© 1987 American Society of Plant Biologists

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Metabolism and Enzymology

Characterization of Nitrate Reductases from Corn Leaves (Zea mays cv W64AxW182E) and Chlorella vulgaris1

Sensitivity to a Proteinase Extracted from Corn Roots

M. Poulle2, Ann Oaks, P. Bzonek3, V. J. Goodfellow and L. P. Solomonson4

Biology Department, McMaster University, Hamilton, Ontario L8S 4K1 Canada

The sensitivity of the two forms of nitrate reductase, NRI and NRII, obtained from the primary leaf of corn, to a limited action corn root proteinase has been examined. The corn inactivating protein (CIP) inhibited the overall reaction (NADH-NR) and the two partial reactions, cytochrome c reductase and reduced methyl viologen NR (MV-NR) of both forms of NR. NADH-cytochrome c reductase was more sensitive to the protease than MV-NR. NRII was less sensitive to inactivation than NRI. When NRI and NRII were inactivated and then subjected to native gel electrophoresis the protein bands associated with MV-NR activity shifted from an Rm value of 0.32 to 0.61 for NRI and from an Rm of 0.28 to 0.60 for NRII. For Chlorella NR these values are 0.32 and 0.70. The initial cleavage of the 116 kilodalton subunit of NRI yielded fragments of 84 and 80 kilodaltons after a 5 minute incubation with CIP. With longer incubation times smaller fragments were also identified. For the Chlorella NR the initial cleavage products are approximately 68 and 25 kilodaltons. Longer incubation times also led to smaller fragments. The products of hydrolysis by this limited action protease are quite different for the corn and Chlorella NRs.

2 Current address: Cereal Crop Research Unit, Barley and Malt Laboratory, 501 N Walnut St., Madison, WI 53705.

3 Supported by a N.S.E.R.C. undergraduate summer scholarship.

4 Current address: Dept. of Biochemistry, College of Medicine, University of South Florida, Tampa, FL 33612.

1 Research supported by an operating grant from N.S.E.R.C. of Canada (A2818) and from NSF (OMB-86-46594).






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Copyright © 1987 by the American Society of Plant Biologists