The Chl a Carboxylic Biosynthetic Routes: Reactions Between Mg-Protoporphyrin IX and Protochlorophyllide a - Chlorophyll Biosynthesis and Technological Applications - page 196

Fig. 7.1 The
heterogeneous
Mg-Proto Pool
the structure of Mg-Proto was ascertained by chemical derivatization coupled to
fluorescence spectroscopy. The conversion of DV and MV Mg-proto to DV and
MV Pchlide a respectively was demonstrated by Tripathy and Rebeiz ( 1986 ).
Molecular biological studies of Mg-Proto chelatase have not yet addressed
the problem of the spatial and chemical heterogeneities of Mg-Proto formation.
The proportion of DV to MV Mg-Proto biosynthesis depends upon the greening
group affiliation of plants, the plants species, and pretreatment of plant tissues.
For example cucumber cotyledons a dark divinyl- light divinyl-light dark divinyl
(DDV-LDV-LDDV) plant tissue(Abd-El-Mageed et al. 1997 ), pretreated with 2,2-
0 -dipyridyl (Dpy) accumulate more DV than MV Mg-Proto in darkness. On the
other hands, more MV Mg-Proto is formed in dark monovinyl-light divinyl-light
dark-monovinyl (DMV-LDV-LDMV) plants such as etiolated corn or barley
(Tripathy and Rebeiz 1986 ).
It has recently become apparent that the DV-MV biosynthetic heterogeneity of
the carboxylic Chl a biosynthetic routes originates in the various Mg-Proto pools
instead of the Proto pool (Kim and Rebeiz 1996 ). Indeed with the development of
improved techniques for the extraction and determination of DV and MV Proto
(Rebeiz 2002 ), it was shown that under no circumstances was it possible to induce
the formation of MV Proto from ALA or from DV Proto in higher plants tissues.
However the conversion of exogenous DV Mg-Proto to MV Mg-Proto in organello
(Kim and Rebeiz 1996 ) was readily achieved.
7.1.1.1 The Divinyl (DV) Mg-Proto Pools
Divinyl Mg-Proto has two vinyl groups at positions 2 and 4 of the tetrapyrrole
macrocycle (Fig. 7.2 ). The DV nature of the DV Mg-Proto component of the