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REGULATION OF PHENYLALANINE AMMONIA‐LYASE ENZYME IN ANNONA FRUIT: KINETIC CHARACTERISTICS AND INHIBITORY EFFECT OF AMMONIA
Author(s) -
MALDONADO R.,
GOÑI O.,
ESCRIBANO M.I.,
MERODIO C.
Publication year - 2007
Publication title -
journal of food biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 47
eISSN - 1745-4514
pISSN - 0145-8884
DOI - 10.1111/j.1745-4514.2007.00106.x
Subject(s) - phenylalanine ammonia lyase , chemistry , phenylalanine , ammonia , enzyme , substrate (aquarium) , cooperativity , enzyme assay , food science , biochemistry , stereochemistry , amino acid , biology , ecology
In this work, we analyzed the kinetic properties of phenylalanine ammonia‐lyase (PAL) extracted from “cherimoya” ( Annona cherimola Mill.) fruits ripened at ambient temperature (20C) and stored under several environmental conditions, including high CO 2 levels (20%) and low temperature (6C). The effect of different ammonia‐related compounds on cherimoya PAL activity was also evaluated. PAL exhibited two different K m values for L‐phenylalanine (L‐Phe ) and negative substrate cooperativity, with Hill coefficient ( n app ) values reaching 0.64 and 0.71 for low temperature and high CO 2 levels, respectively. The kinetic analysis revealed that ammonia produced mixed inhibition of PAL enzyme, with inhibition constants ( K i and K i ′) values of 0.57 ± 0.2 mM and 2.54 ± 0.2 mM. We propose that the regulation of PAL by ammonia inhibition and the negative cooperativity may be essential in adjusting the active phenylpropanoid metabolism in Annonas to the requirement of L‐Phe and in consequence, to the carbon skeleton demand for other anabolic pathways.