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A new type of chlorophyll catabolite was isolated from extracts of de-greened primary leaves of barley (Hordeum vulgare cv. Lambic). Its constitution was elucidated by one-dimensional and two-dimensional { 1 H, 13C}-homoand heteronuclear NMR spectroscopic techniques and by high resolution mass spectroscopy. The isolated catabolite, a water-soluble, colorless, and nonfluorescent linear tetrapyrrole, resembles urobilinogen in which one of the propionic side chains forms a five membered isocylic ring system, indicating its origin from the chlorophylls.Metabolic disappearance of the chlorophylls (Chls) 1 in phototrophic organisms indicates programmed close down of photosynthesis. Although several linear tetrapyrrolic Chl catabolites were isolated during the last decade from green algae and higher plants, the metabolic pathway of tremendous amounts of the Chls is still under question. What products follow after the familiar formybilinones? What are the ultimate products of Chl degradation? Degradation of the Chls occurs in light as well as in darkness. During senescence cellular components are hydrolyzed and metabolized; liberated rare elements such as [N], [P], [S] and metal ions are relocated (1, 2).The first structures of Chl catabolites isolated from a green alga and a higher plant were published in 1991 (3, 4). Several Chl catabolites have been isolated since then (Fig. 1). The similarity of the structures of the red Chl catabolites (3, 4) isolated from the green alga Chlorella protothecoides with the colorless catabolites isolated from higher plants (5-7) suggest a close relationship in the basic skeleton. Biologists regard members of the phylum Chlorophyta as progenitor of the higher plant cell (9, 10). This information triggered research activities in several disciplines to elucidate the apparently unique catabolic pathway of the Chls in the green plant lineage. The studies range from the elucidation of chemical and enzymatic reaction mechanisms to molecular biological research (6,11,12). Previous labeling experiments with oxygen isotopes and heavy water showed a high regio-and stereoselectivity of the oxidative ring opening mechanism and the involvement of a monooxygenase in the ring cleaving step (13-15). The remarkable allylic pyrroline/pyrrole rearrangement was studied in detail (11,16). Most recent in vivo deuterium labeling has shown that in higher plants Chl b is degraded via Chl a (17).Chl breakdown has long been considered as a detoxification process in which photodynamic active Chls convert to colorless tetrapyrrolic products, all of them carry a characteristic formyl group (Fig. 1). Those products were regarded as the final products of Chl breakdown in senescent plants, which apparently do not cause further cleavage into smaller fragments (6).This work focuses on the isolation and determination of the constitution of a new type of chlorophyll catabolite by spectroscopic methods and discusses the origin and relevance in the catabolic pathway of the chlorophylls in plants. EXPERIMENTAL PROCEDURESGen...

When grown in a medium rich in glucose but poor in nitrogen. the algae C/dure/lr protorhecoides excrete a red pigment the structure of which has been proven to correspond IO a product of osydative ring cleavage of the chlorophyll-u chromophore at the C4-C5 methine bridge.Chlorophyll-cr catabolism: l9-Formyl-1[2lH. 22Hlbilinon derivative

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Only recently have products of the enzymatic breakdown of the chlorophylls been characterized for the first time. All catabolites isolated until now from a chlorophyte and from angiosperms have in common the position at which the primary oxygenative ring cleavage occurs, yielding linear tetrapyrroles (19-formyl-l[21H,22H]bilinones). In vivo studies of masO 2 incorporation in one of the chlorophyll catabolites isolated from Chlorella prototheeoides show unequivocally that of the two oxygen atoms inserted into the pigment, only the formyl oxygen originates from dioxygen whereas the other one, the lactamic oxygen atom, derives from water. These findings suggest a monooxygenase-catalyzed primary process in the catabolism of chlorophyll.