Primary fluorescent chlorophyll catabolites

RCC is very unstable and rapidly reduced to a primary fluorescent chlorophyll catabolite (pFCC) by red chlorophyll catabolite reductase (RCCR). In subsequent steps pFcc is converted to different fluorescent chlorophyll catabolites (FCCs). These chemically rather labile compounds are further converted into colorless nonfluorescing chlorophyll catabolites (NCCs) by a nonenzymatic deconjugation of the four... 

Scheme 1. Overview of chlorophyll breakdown in senescent higher plants (2). The chlorophylls (Chi a, la (R = CH3) or Chi b, lb (R = CH=0) are degraded via pheophorbide a (Pheo a, 5a), red chlorophyll catabolite (RCC, 11), the primary fluorescent chlorophyll catabolites (pFCCs, 10) to non-fluorescent chlorophyll catabolites (NCCs), such as //v-NCC-1 (2, also called RP-14)...

Scheme 5. In higher plants pheophoibide a (5a) is degraded to the primary fluorescent chlorophyll catabolite (pFCC, 10) and to its C(l)-epimer epi-10 (epi-pFCC)...

The red chlorophyll catabolite RCC (11) is bound strongly to PaO and inhibits it. In an in vitro assay, the soluble reductase from oilseed rape converted 11 to the primary fluorescent chlorophyll catabolite pFCC (10, 31,32-didchydro-1,4,5,10,17,18,20-(22//)-octahydro-132-(mcthoxy-carbonyl)-4,5-dioxo-4,5-seco-phytoporphyrin) (62, 83). The reductase, which was named red chlorophyll catabolite reductase (RCC-reductase) (68, 80, 83), introduced the chiral center C(l) via a stereo-selective reduction step. However, early studies with oilseed rape and sweet pepper indicated a remarkable stereo-dichotomy of the respective reductases (see above) (67, 68, 69). Screening of a variety of plant species for their type of primary FCC revealed the broad existence of two classes of the RCC-reductases , whose stereo-selectivity was species specific (84). At present, the (absolute or relative) configuration at C(l) in the two pFCCs (10 and epi-10) is not yet established (2). Indeed, the existence of the two epimeric pFCCs (10 and epi-10) (see Scheme 6) indicated the absolute configuration at the newly generated chiral center to have no apparent functional relevance (67, 68, 69). 

Scheme 6. Primary fluorescent catabolites (pFCCs) 10 and epi-10 result from enzymatic reduction of the elusive red chlorophyll catabolite (RCC, 11) by RCC-reductase...

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