Environmental Engineering Reference
In-Depth Information
Fig. 4
Representative structural outline of major catabolites delineating the main paths of chlo-
rophyll breakdown in higher plants (Kräutler and Hörtensteiner
2006
; Moser et al.
2009
): Chls
are degraded in the chloroplast by enzyme-catalyzed processes via pheophorbide (Pheide)
a
and
the red chlorophyll catabolite (RCC) to give primary fluorescent chlorophyll catabolites (
p
FCC,
or its C1-epimer, epipFCC). The relevant enzymes involved in this part are: (
a
) Chl
b
reductase;
(
b
) 7-hydroxymethyl Chl reductase; (
c
) chlorophyllase (CLH); )
d
) 85magnesium dechelatase; (
e
)
pheophytinase (PPH); (
f
) Pheide
a
oxygenase (PAO); (
g
) RCC reductase (RCCR).
p
FCCs are
modified further by unidentified hydroxylating enzymes (
h
,
i
). When carrying a free propionic
acid group, FCCs are transported into the vacuole, where they are suggested to isomerize by a
spontaneous, acid catalyzed reaction (
j
) to the corresponding nonfluorescent chlorophyll catabo-
lites (NCCs), such as Hv-NCC-1 (the main tetrapyrrolic catabolite found in senescent leaves of
barley, Hordeum vulgare). Else, they are esterified by unknown enzymes at the propionic acid
group (
k
) to give 'persistent' hypermodified FCCs, such as Mc-FCC-56 (the main FCC in peels
of ripe bananas, Musa acuminata, cavendish cultivar). Relevant atom numbering is specified
Data source
Hörtensteiner and Kräutler (
2011
)
hydrolysis of a phytol residue in ring IV, catalyzed by the enzyme chlorophyllase
that converts Chl to phytol and chlorophyllide (Drazkiewicz
1994
; Jacob-Wilk
et al.
1999
; Tsuchiya et al.
1999
; Willstätter and Stoll
1913
; Trebitsh et al.
1993
;
Schelbert et al.
2009
). The 'Mg dechelatase' subsequently occurs in chlorophyl-
lide, by displacement with 2 H
+
(dechelation) that produces pheophorbide. The
latter is subsequently cleaved by an oxygenase enzyme and converted into red
Chl catabolite (RCC). Subsequent reduction can produce colorless primary fluo-
rescent Chl catabolite (
p
FCC). The in vivo and in vitro accumulation of pheopig-
ments during Chl degradation in algae and higher plants suggests the presence
of a 'magnesium dechelatase' enzyme (Owens and Falkowskit
1982
; Shioi et al.
