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Titolo:
MONOPHENOLASE ACTIVITY OF POLYPHENOL OXIDASE FROM VERDEDONCELLA APPLE
Autore:
ESPIN JC; MORALES M; VARON R; TUDELA J; GARCIACANOVAS F;
Indirizzi:
UNIV MURCIA,FAC BIOL,DEPT BIOQUIM & BIOL MOLEC A E-30100 ESPINARDO SPAIN UNIV CASTILLA LA MANCHA,ESCUELA UNIV POLITECN ALBACETE,DEPT QUIM FIS ALBACETE SPAIN
Titolo Testata:
Journal of agricultural and food chemistry
fascicolo: 11, volume: 43, anno: 1995,
pagine: 2807 - 2812
SICI:
0021-8561(1995)43:11<2807:MAOPOF>2.0.ZU;2-V
Fonte:
ISI
Lingua:
ENG
Soggetto:
MELANIN BIOSYNTHESIS PATHWAY; PARTIAL-PURIFICATION; ENZYMATIC OXIDATION; PHASE-SEPARATION; TRITON X-114; L-PROLINE; L-SERINE; TYROSINASE; 4-METHYLCATECHOL; MELANIZATION;
Keywords:
APPLE; TYROSINASE; POLYPHENOL OXIDASE; ENZYME KINETICS; MONOPHENOLS; HYDROXYPHENYLPROPIONIC ACID; MBTH;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
43
Recensione:
Indirizzi per estratti:
Citazione:
J.C. Espin et al., "MONOPHENOLASE ACTIVITY OF POLYPHENOL OXIDASE FROM VERDEDONCELLA APPLE", Journal of agricultural and food chemistry, 43(11), 1995, pp. 2807-2812

Abstract

Apple polyphenol oxidase (PPO) has been isolated and partially purified by using two sequential phase partitionings with Triton X-114 reported here for the first time. The enzyme showed monophenolase activity when assayed on (p-hydroxyphenyl)propionic acid (PHPPA) with 3-methyl-2-benzothiazolinone hydrazone (MBTH) in a new and reliable continuous spectrophotometric method, with high sensitivity, accuracy, and precision. The initial monophenolase activity showed a lag period (tau) prior to the attainment of the steady state rate (V-ss). Both kinetic parameters, tau and V-ss, depended on the pH, the enzyme and substrate concentrations, and the presence of catalytic amounts of o-diphenol. These dependencies can be explained in terms of a reaction mechanism involving one single active site, two enzyme forms, E(met) and E(oxy), and a set of nonenzymatic reactions from o-quinones to chromophoric MBTH-quinone adduct, with regeneration of one molecule of o-diphenol. The effect of pH was related with two significant pK(a) values of the free enzyme forms but not of enzyme-substrate complexes. This kinetic characterization was essential for understanding and choosing optimal assay conditions for determining enzyme activity and concentration when using PHPPA as a monophenolic substrate of apple PPO.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 29/11/20 alle ore 00:16:45