Pigment-free NADPH:protochlorophyllide oxidoreductase from Avena sativa L. Purification and substrate specificity.
The enzyme NADPH:protochlorophyllide oxidoreductase ( POR) is the key enzyme for light-dependent chlorophyll biosynthesis. It accumulates in dark-grown plants as the ternary enzyme-substrate complex POR-protochlorophyllide a-NADPH. Here, we describe a simple procedure for purification of pigment-free POR from etioplasts of Avena sativa seedlings. The procedure implies differential solubilization with n-octyl-beta-D-glucoside and one chromatographic step with DEAE-cellulose. We show, using pigment and protein analysis, that etioplasts contain a one-to-one complex of POR and protochlorophyllide a. The preparation of 13 analogues of protochlorophyllide a is described. The analogues differ in the side chains of the macrocycle and in part contain zinc instead of the central magnesium. Six analogues with different side chains at rings A or B are active substrates, seven analogues with different side chains at rings D or E are not accepted as substrates by POR. The kinetics of the light-dependent reaction reveals three groups of substrate analogues with a fast, medium and slow reaction. To evaluate the kinetic data, the molar extinction coefficients in the reaction buffer had to be determined. At concentrations above 2 mole substrate/mole enzyme, inhibition was found for protochlorophyllide a and for the analogues.[1]References
- Pigment-free NADPH:protochlorophyllide oxidoreductase from Avena sativa L. Purification and substrate specificity. Klement, H., Helfrich, M., Oster, U., Schoch, S., Rüdiger, W. Eur. J. Biochem. (1999) [Pubmed]
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