Biology Reference
In-Depth Information
65,000. The bovine enzyme has a tightly bound FAD prosthetic group. The plant
enzyme has been partially characterized (Jacobs and Jacobs
1987
). Protox was
recently purified form spinach chloroplasts (Watanabe et al.
2000
). Its molecular
weight was estimated at 60 kDa by SDS-PAGE.
Diphenyl ether herbicides inhibit Protox (Matringe and Scalla
1988
) and result
in the accumulation of Protogen IX which translocates to various part of the cell
(Lehnen et al.
1990
). When Protogen is converted to Proto at various cellular sites,
cell death ensues in the light in a typical porphyrin-dependent photodynamic
herbicidal phenomenon (Rebeiz et al.
1984
). In animal cells, during heme biosyn-
thesis, Protogen IX is converted to Proto in the mitochondria. In plant cells, Protox
appears to be loosely bound to the plastid membranes (Lee et al.
1991
).
5.6.2 Biosynthetic Heterogeneity of Protoporphyrin IX
In cucumber cotyledon and barley leaves chloroplasts, multiple Proto sites appear
to be involved in resonance excitation energy transfer to the Chl
a
of LHCII, the
major thylakoid LHC antenna, to LHCI-680, one of the inner LHC antennae of PSI,
to Chl
a
of CP47 and CP29, two PSII antennae and to LHCI-73 an inner PSI
antenna. This has led to the conclusion that the various Proto pools exist in different
environments in the thylakoid membranes (Table
5.1
) and (Kopetz et al.
2004
).
This observation together with an apparent ALA biosynthetic heterogeneity
(Averina et al.
1993
; Averina
1998
), has led to the proposal of five different
Proto biosynthesis sub-locations in thylakoid membranes. It is uncertain at this
stage whether or not the 5 sub-locations contain identical enzymes that catalyze
the conversion of ALA to Proto or not. In other words it is still uncertain whether
the spatial heterogeneity of Proto formation is accompanied by biosynthetic
heterogeneity.
References
Akhtar M (1994) The modification of acetate and propionate side chains during the biosynthesis of
haem and chlorophylls: mechanistic and stereochemical studies. In: The biosynthesis of
tetrapyrrole pigments. Ciba Foundation symposium, vol 180. Wiley, Chichester, pp 131-155
Averina NG (1998) Mechanisms of regulation and interplastid location of chlorophyll biosynthesis.
Biol Membr 15(5):504-516
Averina NG, Rudoi AB, Fradkin LI (1993) Centers of chlorophyll biosynthesis - current notions.
Biofizika 38(6):1082-1086
Battersby AR, Donald MC, Redfern JR et al (1976) Biosynthesis of porphyrins and related
macrocycles. V. Structural integrity of the type III porphyrinogen macrocycle in an active
biological system; studies on the aromitazation of protoprphyrin-IX. J Chem Soc Perkins Trans
1:266-273
Battersby AR, Fookes CJR, Matcham GWJ et al (1979) Order of assembly of the four pyrrole rings
during the biosynthesis of the natural porphyrins. J Chem Soc Chem Commun:539-541
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