tailieunhanh - Báo cáo Y học: The effects of low pH on the properties of protochlorophyllide oxidoreductase and the organization of prolamellar bodies of maize (Zea mays)

Prolamellar bodies (PLB) contain two photochemically active forms of the enzyme protochlorophyllide oxidoreductase POR-PChlide640 and POR-PChlide650 (the spectral forms of POR-Chlide complexes with absorption maxima at the indicated wavelengths). Resuspension of maize PLB in media with a pH below leads to a rapid conversion of POR-PChlide650 to POR-PChlide640 and a dramatic re-organization of the PLB membrane system. In the absence of excess NADPH, the absorption maximum of the POR complex undergoes a further shift to about 635 nm | Eur. J. Biochem. 269 2336-2346 2002 FEBS 2002 doi The effects of low pH on the properties of protochlorophyllide oxidoreductase and the organization of prolamellar bodies of maize Zea mays Eva Selstam1 Jenny Schelin1 Tony Brain2 and W. Patrick Williams2 1 Umea Plant Science Center Department of Plant Physiology University of Umea Sweden 2Life Sciences Division King s College University of London UK Prolamellar bodies PLB contain two photochemically active forms of the enzyme protochlorophyllide oxido-reductase POR-PChlide640 and POR-PChlide650 the spectral forms of POR-Chlide complexes with absorption maxima at the indicated wavelengths . Resuspension of maize PLB in media with a pH below leads to a rapid conversion of POR-PChlide650 to POR-PChlide640 and a dramatic re-organization of the PLB membrane system. In the absence of excess NADPH the absorption maximum of the POR complex undergoes a further shift to about 6135 nm. This latter shift is reversible on the re-addition of NADPH with a half-saturation value of about mM NADPH for POR-PChlide640 reformation. The disappearance of POR-PChlide650 and the reorganization of the PLB however are irreversible. Restoration of low-pH treated PLB to pH leads to a further breakdown down of the PLB membrane and no reformation of POR-PChlide650. Related spectral changes are seen in PLB aged at room temperature at pH in NADPH-free assay medium. The reformation of POR-PChlide650 in this system is readily reversible on re-addition of NADPH with a half-saturation value about M. Comparison of the two sets of changes suggest a close link between the stability of the POR-PChlide650 membrane organization and NADPH binding. The low-pH driven spectral changes seen in maize PLB are shown to be accelerated by adenosine AMP ADP and ATP. The significance of this is discussed in terms of current suggestions of the possible involvement of phosphorylation or adenylation in changes in the .