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Plant and Cell Physiology, 1986, Vol. 27, No. 8 1499-1506
© 1986

Article

Kinetics of Phenylalanine Ammonia-Lyase and the Effect of L-{alpha}-aminooxy-ß-phenylpropionic Acid on Enzyme Activity and Radicle Growth in Germinating Lettuce Seeds1

G. Jose Kudakasseril2 and Subhash C. Minocha3

2Dept. of Biology, Kenyon College Gambier, OH 43022, U.S.A.
3University of New Hampshire, Department of Botany & Plant Pathology, Nesmith Hall Durham, New Hampshire, 03824 U.S.A.

The effects of different concentrations of L-{alpha}-aminooxy-ß-phenyIpropionic acid (AOPP), an analog of L-phenylalanine, on the activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5 [EC] ) and the growth of radicles in 24 h old germinating lettuce (Lactuca saliva L.) seeds were investigated. AOPP causes a significant inhibition of PAL activity in the seeds (85% inhibition at 104 M). It also causes a stimulation of radicle growth at that concentration. The results show that the inhibition of PAL by AOPP may be due to an irreversible binding of the inhibitor to the enzyme leading to its inactivation. AOPP also inhibits ethylene biosynthesis in germinating lettuce seeds which could probably explain the stimulation of radicle growth in these seeds.

The enzyme shows typical Michaelis-Menten kinetics. The Km for L-phenylalanine is 4.2 x 105 M. The enzyme does not show any tyrosine ammonia-lyase activity. Various substrate analogs such as D-phenylalanine, p-fluorophenylalanine, ß-phenyllactic acid, tryptophan and the product of the enzyme reaction, trans-cinnamic acid, inhibit the enzyme competitively. A number of intermediates and endproducts of the phenylpropanpid pathway, except chlorogenic acid, do not show any inhibition.

1Scientific contribution number 1423 from the New Hampshire Agricultural Experiment Station.

(Received May 9, 1986; Accepted September 8, 1986)
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