Detection of 1-aminocyclopropane-1-carboxylate oxidase activity in seeds of Stylosanthes humilis H.B.K

• Autor(a) principal: Barros,Raimundo Santos
• Data de Publicação: 2013
• Outros Autores: Pinheiro,Frank James Araújo, Müller,Caroline, Pires,Marcel Viana, Silva,Alexei Gresta Vieira da, Ribeiro,Dimas Mendes
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Theoretical and Experimental Plant Physiology
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S2197-00252013000300008
• topic: dioxygenase; enzymatic kinetics; ethylene; inhibition; ACO

The activity of 1-aminocyclopropane-1-carboxylate oxidase (ACO) was characterized in seeds of the tropical legume Townsville stylo (Stylosanthes humilis) both in vitro (desalted extract of non-dormant seeds) and in vivo (entire dormant seeds). Optimum conditions for maximum in vitro ACO activity in a Trizma-HCl 100 mM buffered medium were: pH 7.0, temperature 32ºC and cofactors and co-substrate at the following concentrations: NaHCO3 30 mM, sodium ascorbate 30 mM and FeSO4 50 µM. Rates of in vitro reaction catalyzed by ACO were shown to be constant within the interval 15-150 minutes from the onset of the reaction. The apparent Km for in vitro ACO, as determined from the non-linear curve fitting to the Michaelis-Menten equation, was 156±8.3 µM ACC with a Vmax 5.4±0.08 mmol (ET) g-1 h-1 on a fresh matter (FM) basis. In vivo (control basal medium: HCl-KOH 10 mM pH 7.0, 30ºC, reaction time 15 hours) apparent Km was 230±27 µM ACC and Vmax 11.9±0.38 mmol (ET) g-1.h-1 on a FM basis. These data suggest that the enzyme exhibits a relatively low affinity for the substrate. The well-known inhibitors of ACO activity, α-aminoisobutyric acid, salicylic and acetylsalicylic acids, n-propylgallate and cobaltous ions, were highly effective in inhibiting ACO activity of Townsville stylo seeds.