RESUMO
Linoleic acid hydroperoxide isomerase was extracted from corn germ and partially purified by differential centrifugation. This enzyme catalyzed the isomerization of linoleic acid hydroperoxide.(see article) Isomerase also catalyzed the substitution of various reagents at the carbon bearing the hydroperoxide group. These fatty acid products had the following functional groupings: (see article) where X is either oleoyloxy, ethylthio, or methoxy resulting from the presence of oleic acid, ethanethiol, or methanol, respectively. A crude wheat germ extract containing both lipoxygenase and isomerase enzymes reacted with linoleic acid to yield alpha-ketols, gamma-ketols, and a substitution product, the linoleoyloxy ester of alpha-ketol. Characterization of these products from wheat germ enzymes showed that the substitution reaction was not unique to corn germ. Because anions of the reagents tested are typical nucleophiles, the substitution reactions may proceed by a nucleophilic mechanism as mediated by the isomerase enzyme.
Assuntos
Isomerases/metabolismo , Ácidos Linoleicos , Peróxidos , Plantas/enzimologia , Sementes/enzimologia , Triticum/enzimologia , Zea mays/enzimologiaRESUMO
We have shown unequivocally that the positional specificity of gamma-ketol formation by a corn germ enzyme was different from that observed previously by others with an alfalfa seedling enzyme. When the pure positional isomers of linoleic acid hydroperoxide served as substrates, the corn germ enzyme formed one of two gamma-ketols: 12-oxo-9-hydroxy-trans-10-octadeconoic acid from 13-hydroperoxys-10-octadecenoic acid from 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid (99+% pure) and 10-oxo-13-hydroxy-trans-11-octadecenoic acid from 9-hydroperoxy-trans-10,cis-12-octadecadienoic acid (96% pure). Also isolated from these reactions was one of two alpha-ketols commonly found as a result of catalysis by linoleic acid hydroperoxide isomerase: 12-oxo-13-hydroxy-cis-9-octadecenoic acid from the 13-hydroperoxide and 10-oxo-9-hydroxy-cis-12-octadecenoic acid from the 9-hydroperoxide. Evidence is offered that gamma-ketol formation is catalyzed by linoleic acid hydroperoxide isomerase, the same enzyme responsible for alpha-ketol production.
Assuntos
Isomerases/metabolismo , Ácidos Linoleicos/metabolismo , Plantas/enzimologia , Hidroxiácidos/metabolismo , Oxirredutases Intramoleculares , Isomerismo , Cetoácidos/metabolismo , Modelos Químicos , Ácidos Oleicos/metabolismo , Peróxidos/metabolismo , Sementes/enzimologia , Estereoisomerismo , Zea mays/enzimologiaAssuntos
Cromatografia em Camada Fina , Nucleotídeos/análise , Azirinas , Celulose , Cloretos , Lítio , PolietilenosAssuntos
Ácidos Graxos Insaturados , Oxigenases , Peróxidos , Sementes/enzimologia , Álcoois , Sulfato de Amônio , Cromatografia Gasosa , Cromatografia em Camada Fina , Eletroforese em Gel de Poliacrilamida , Concentração de Íons de Hidrogênio , Lipídeos , Espectrometria de Massas , Rotação Ocular , Oxirredução , Oxigenases/isolamento & purificação , Glycine max , Especificidade da Espécie , Espectrofotometria Infravermelho , Estereoisomerismo , Zea mays/enzimologiaRESUMO
Protein-rich subcellular particulates were isolated by zonal centrifugation from homogenates of endosperms of normal, opaque-2, and floury-2 mutant corn (Zea maize) kernels at different stages of development. In early stages the high lysine mutants vary from normal corn by greater production of a glutelin protein not associated with the matrix. This protein is high in lysine and may become a component of matrix glutelin at later stages of maturity. Differences in size and structure of zein-rich protein bodies were observed in the mutant strains when compared with normal corn. Enhanced production of nonmatrix glutelin as well as the reduction in synthesis of lysine-deficient zein is responsible for the improved lysine content of the mutant endosperms at early stages of development.