Biology Reference
In-Depth Information
Fig. 7.13 MV Mg-Proto
monomethyl ester
(MV Mpe)
Metabolism of DV Mpe in LMV-DDV-LDMV Plants Species
The specific role of DV Mpe as a precursor of DV Pchlide a in DDMV-LDV-LDMV
plant species was demonstrated by conversion of exogenous DV Mpe to DV Pchlide
a in isolated etiochloroplasts of barley (Tripathy and Rebeiz 1986 ), a DMV-LDV-
LDMV plant species (Abd-El-Mageed et al. 1997 ). In barley etioplasts, DVMpe was
converted into 44 % DV Pchlide a , and 56 % MV Pchlide a .
To our knowledge, no kinetic studies have been performed on SAMMT purified
to homogeneity, with pure MV Mpe. Since the mechanism of action of SAMMT
has been reported to vary i. e. ping pong (Ellsworth et al. 1974 ), random Bi Bi
(Ebbon and Tait 1969 ), or ordered Bi Bi (Hinchigeri et al. 1984 ) depending on the
source of enzyme, it is not possible to assign with certainty a precise mechanism for
its action without precise knowledge of the DV or MV nature of the Mpe substrate.
7.2.1.2 The MV Mpe Pool
Monovinyl Mg-Proto monomethyl ester has one vinyl groups at positions 2 and one
ethyl group at position 4 of the tetrapyrrole macrocycle (Fig. 7.13 ). The MV nature
of the MV Mpe pool was ascertained by chemical derivatization coupled to
analytical fluorescence spectroscopy at 77 K (Belanger and Rebeiz 1982 ).
Biosynthesis of MV Mpe in DDV-LDV-LDDV Plant Species
In DDV-LDV-LDDV plant species, MV Mg-Proto is formed from DV Mg-Proto by
reduction of the vinyl group to ethyl at position 4 (ring B) of the macrocycle in one
thylakoid environment (Fig. 7.14 ) (Kim and Rebeiz 1996 ; Kolossov and Rebeiz
2010 ). By similarity with DDV-LDV-LDMV plants such as barley (see below),
The reaction is probably catalyzed by a [4-vinyl] Mpe reductase (4VMPR) (Kolossov
and Rebeiz 2010 ).
The presence of this enzyme in DDV-LDV-LDDV plant species such as cucumber
is strongly suggested by the biosynthesis and accumulation of MV Pchlide a during
incubation of MV Proto in isolated cucumber etiochloroplasts (Tripathy and
Rebeiz 1986 ).
Search WWH ::




Custom Search