title: Pigment-free NADPH:protochlorophyllide oxidoreductase from Avena sativa L. Purification and substrate specificity.
abstract: 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.
authors.affiliation: Botanisches Institut der Ludwig-Maximilians-Universität München, Munich, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Klement
authors.forename: M
authors.initials: M
authors.lastname: Helfrich
authors.forename: U
authors.initials: U
authors.lastname: Oster
authors.forename: S
authors.initials: S
authors.lastname: Schoch
authors.forename: W
authors.initials: W
authors.lastname: Rüdiger
mesh_terms: D018554:Avena / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D010088:Oxidoreductases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010777:Photochemistry; D011521:Protochlorophyllide / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D013053:Spectrophotometry; D013379:Substrate Specificity
chemical_list: D011521:Protochlorophyllide; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase