Biology Reference
In-Depth Information
Table 6.1
(continued)
Conc
Excitation resonance energy maxima
to:
ALA Dpy
Donor conc
(pmoles/ml
suspension)
Plant
species
Major
donor
Chl
a
F686
Incub
(h)
Chl
a
F694 Chl
a
F738
(mM)
Barley
MV
Pch-
lide
a
104
439p,
445s,
450p,
458p,
463s
436s, 447p,
455p,
463s
440p, 450p,
458p
20
4
6
Barley
MV
Pch-
lide
a
193
439s,
444p,
451p,
462p,
467p
435s, 440s,
446p,
453p,
460p
438s, 453p,
457p,
464s
20
0
6
Organic life in the biosphere is made possible by consumption of the chemical
energy generated by photosynthesis.
Hemes are the prosthetic groups of cytochromes which are involved in electron
transport during oxidative phosphorylation and photosynthetic phosphorylation
which generate ATP and NADPH. The latters are essential for many cellular
functions.
The importance of heme and Chl to life in the biosphere will be stressed in
several chapters of this monograph.
6.2.3 Mg-Protoporphyrin IX Chelatase
6.2.3.1 Mg Insertion into Protoporphyrin IX
The enzymatic insertion of Mg into Proto by Mg-Proto chelatase, to yield Mg-Proto
was achieved in organello (Smith and Rebeiz
1977a
,
b
). At the low ATP
concentrations used in this system, the biosynthesis of Mg-Proto was accompa-
nied by the formation of Zn-Proto. Simultaneous equations were used in order
to deconvolute the fluorescence spectra and be able to determine the amounts of
Mg-Proto in the presence of Zn-Proto contamination (Smith and Rebeiz
1977a
,
b
).
Later on, interference from Zn-Proto was eliminated when it was realized that
ATP was a mandatory cofactor for Mg-insertion into Proto and that higher concen-
tration of added ATP eliminated the Zn-Proto problem formation (Pardo
et al.
1980
) (Fig.
6.6
)
In cucumber etiochloroplasts, Mg-Proto chelatase is bound to the plastid
membranes (Lee et al.
1991
,
1992
; Smith and Rebeiz
1979
). The activity of the
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