Comparison of homoserine dehydrogenase from different plant sources |
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Authors: | S Grego D Tricoli G Di Marco |
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Institution: | Laboratorio di Radiobiochimica ed Ecofisiologia Vegetali, Consiglio Nazionale delle Ricerche, Area della Ricerca, Monterotondo Scalo 00016, Rome, Italy |
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Abstract: | Homoserine dehydrogenase (HSD) was partially purified from castor bean, pea and wheat seedlings. The enzyme from pea had a MW of 75 000 and no sensitivity to threonine when measured in the direction of homoserine formation (forward reaction). The enzyme purified from castor bean had a MW of 290 000–350 000 and exhibited an almost complete inhibition by 1 mM threonine. Furthermore, this enzyme exhibited a polymeric nature as shown by polyacrylamide electrophoresis of the desensitized preparation and by SDS electrophoresis of the native enzyme. In wheat two isoenzymes were separated by gel filtration on Sephadex G 200. The fast-moving fraction (HSD I) was completely inhibited by threonine and exhibited a MW of 280 000, while the slow-moving fraction (HSD II) was insensitive to threonine and had a MW of 75 000. The sensitive enzyme from wheat and castor bean showed an almost absolute requirement for K+. The enzyme from pea and the insensitive form from wheat did not show a requirement for K+. For the wheat enzyme the effect of several amino acids and the main kinetic constants were studied. |
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Keywords: | Leguminosae pea Euphorbiaceae castor bean Graminae wheat homoserine dehydrogenase threonine |
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