Chlorophyll b to Chlorophyll a Conversion Precedes Chlorophyll Degradation in Hordeum vulgare L.

• Published in: The Journal of biological chemistry 1999-07, Vol.274 (31), p.21811-21816
• Main Authors: Folly, Patrick, Engel, Norbert
• Format: Article
• Language: English
• Subjects: chemical structure; chlorophyll; Chlorophyll - chemistry; Chlorophyll - metabolism; Chlorophyll A; dark; Darkness; degradation; Deuterium Oxide; Hordeum - metabolism; Hordeum vulgare; Kinetics; Magnetic Resonance Spectroscopy; metabolism; Models, Molecular; Molecular Structure; nuclear magnetic resonance spectroscopy; Plant Leaves - metabolism; reduction; spectral analysis; Spectrometry, Mass, Secondary Ion
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.274.31.21811

This study reveals by in vivodeuterium labeling that in higher plants chlorophyll (Chl)b is converted to Chl a before degradation. For this purpose, de-greening of excised green primary leaves of barley (Hordeum vulgare) was induced by permanent darkness in the presence of heavy water (80 atom % 2H). The resulting Chla catabolite in the plant extract was subjected to chemical degradation by chromic acid. 3-(2-Hydroxyethyl)-4-methyl-maleimide, the key fragment that originates from the Chl catabolite, was isolated. High resolution 1H-, 2H-NMR and mass spectroscopy unequivocally demonstrates that a fraction of this maleimide fragment consists of a mono-deuterated methyl group. These results suggest that Chl b is converted into Chla before degradation. Quantification proves that the initial ratio of Chl a:Chl b in the green plant is preserved to about 60–70% in the catabolite composition isolated from yellowing leaves. The incorporation of only one deuterium atom indicates the involvement of two distinguishable redox enzymes during the conversion.