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Plant Physiology 59:695-700 (1977)
© 1977 American Society of Plant Biologists

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Articles

Characterization of Two Isoenzymes of Lipoxygenase from Bush Beans 1

Gwendolyn B. Hurt2,3 and Bernard Axelrod4

a Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907

Two isoenzymes of lipoxygenase, a and b, have been obtained from bush beans (Phaseolus vulgaris) as electrophoretically homogeneous proteins. Both proteins have a molecular weight of 100,000, contain 1 atom of iron, and appear to be composed of a single peptide chain. However, these enzymes appear to differ in some other respects. Thus, lipoxygenase a has an isoelectric point of 6.03 while lipoxygenase b has a value of 5.57. Their pH optima are 5 to 7 and 6.5 to 7, respectively. Both lipoxygenase a and b, when acting on linoleic acid plus the product hydroperoxide, generate what are presumably keto-dienes with an absorption maximum at 280 nm. Whereas lipoxygenase a can catalyze this secondary reaction in the presence of O2, lipoxygenase b does so only under anaerobic conditions. Lipoxygenase a is stimulated by Ca2+ while lipoxygenase is not. An unexpected finding is the strong inhibition of lipoxygenase a by Mn2+ (50% inhibition at 12.5 µM under standard reaction conditions). Lipoxygenase b is inhibited by Mn2+ but only at concentrations about 250 times greater.

2 This research is a part of a dissertation submitted by G. B. H. in partial fulfillment of the M.S. requirements.

3 Present address: Eli Lilly and Company, Indianapolis, Ind. 46206.

4 To whom reprint requests should be addressed.

1 This work was supported by National Science Foundation Grant No. BMS 13883. Journal Paper No. 6470 from the Purdue Agricultural Experiment Station.






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Copyright © 1977 by the American Society of Plant Biologists