Tyr152 plays a central role in the catalysis of 1-aminocyclopropane-1-carboxylate synthase.
1-Aminocyclopropane-1-carboxylate (ACC) synthase is a key enzyme in the regulation of ethylene biosynthesis in higher plants. To investigate the catalytic significances of two conserved tyrosine residues, Tyr151 and Tyr152, of a tomato ACC synthase isozyme (LeACS2), five ACC synthase mutants (Y151F, Y151G, Y152F, Y152G, and Y151F/Y152F) were constructed and over-expressed in Escherichia coli. Subsequent kinetic analysis indicated that these point mutations in mutants Y152F, Y152G, and Y151F/Y152F, either reduced the catalytic efficiency more than 98% or fully inactivated ACC synthase, while Y151F and Y151G mutants reduced the enzymatic activities by 27% and 83%, respectively. It is therefore concluded that Tyr152, especially its hydroxyl group, plays an essential role in the catalysis of ACC synthase. Thus, a revised catalytic model is hereby proposed for functional ACC synthase.
Li
Jian-Feng
JF
Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China.
Qu
Liang-Hu
LH
Li
Ning
N
D000595:Amino Acid Sequence; D000598:Amino Acids, Cyclic / Q000096:biosynthesis / Q000737:chemistry; D001665:Binding Sites; D002384:Catalysis; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008190:Lyases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D030781:Organisms, Genetically Modified; D012436:S-Adenosylmethionine / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014443:Tyrosine
D000598:Amino Acids, Cyclic; C023863:1-aminocyclopropane-1-carboxylic acid; D014443:Tyrosine; D012436:S-Adenosylmethionine; D008190:Lyases; C021773:1-aminocyclopropanecarboxylate synthase