| Popis: |
Summary Homoserine kinase was partially purified from green shots of 2-week-old pea ( Pisum sativum L. cv. Pillert Fenomen) seedlings. The enzyme had an absolute requirement for both divalent (mg 2+ and Mn 2+ ) and monovalent (K + ) cations. The K m values of homoserine (6.7 mM) and ATp (2.7 mM) were much higher than for the enzyme from barley. The product O -phosphohomoserine was an effective inhibitor of the reaction. Isoleucine, valine and ornithine were potent competitive inhibotors with respect to homoserine with K i values of 0.9 mM, 0.9 mM and 4.3 mM, respetively. Activity was also reduced in the presence of S -adenosylmethionine, this inhibitor giving sigmoidal rate versus concentration plots. Threonine, methionine and lysine, alone or in combination, had little effect. The control propertties of the enzyme were compared to those of homoserine kinases from barley and bacterial sources. |
