Chlorophylls of the c family: absolute configuration and inhibition of NADPH:protochlorophyllide oxidoreductase
2003
Helfrich, M. | Bommer, B. | Oster, U. | Klement, H. | Mayer, K. | Larkum, A.W.D. | Rudiger, W.
Using circular dichroism (CD) spectroscopy, the stereochemistry at C-13(2) of members of the chlorophyll (Chl) c family, namely Chls c1, c2, c3 and [8-vinyl]-protochlorophyllide a (Pchlide a) was determined. By comparison with spectra of known enantiomers, all Chl c members turned out to have the (R) configuration, which is in agreement with considerations drawn from chlorophyll biosynthesis. Except for a double bond in the side chain at C-17, the chemical structure of Chl c1 is identical with Pchlide a, the natural substrate of the light-dependent NADPH:protochlorophyllide oxidoreductase (POR). Thus, lack of binding to the active site due to the wrong configuration at C-13(2), which had been proposed previously, cannot be an explanation for inactivity of Chl c in this enzymic reaction. Our results show rather that Chl c1 is a competitive inhibitor for this enzyme, tested with Pchlide a and Zn-protopheophorbide a (Zn-Ppheide a) as substrates.
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