Biology Reference
In-Depth Information
Fig. 8.2 Intermediate Acrylic, OH and Keto derivatives of Mpe involved in the formation of the
cyclopentanone ring of Pchlide a . The Residue R represents a vinyl group for the DV intermediates
and an ethyl group for the MV intermediates
8.1.1.1 Formation of the Cyclopentanone Ring
Formation of the cyclopentanone ring (ring E) during the proposed conversion of Mpe
to Pchlide a was suggested in 1950 to involve a beta-oxidation of a putative methyl
Propionate side chain to a 3-keto derivative (Granick 1950b ). Later on, detection of
putative DV and MV metal-free acrylic, hydroxy and keto derivatives in ultraviolet
Chlorella mutants, led to the proposal that in lower plants, the formation of DV and
MV Pchlide a involves a beta-oxidation sequence of the methyl propionate of DV
and MV Mpe, at position 6 of the macrocycle and the formation of acrylic, hydroxy,
and keto propionate Mpe intermediates (Ellsworth and Aronoff 1969 ). The authors
suggested that the DV and MV keto methyl propionate species cyclized automatically
to yield DV and MV Pchlide a respectively (Ellsworth and Aronoff 1969 ). This work
was met with skepticism and the putative intermediates were considered to be
artifacts. This feeling was reinforced by the inability of the techniques, used by
Ellsworth and Aronoff as well as of other analytical techniques available at that
time, to detect the proposed MV Mpe substrate (MV Mpe), the proposed DV and
MV acrylic, OH, and keto intermediates, and the DV Pchlide a end product in normal,
green, lower and higher plants (Fig. 8.2 ).
A new phase in the study of the cyclopentanone ring formation was ushered by the
introduction of powerful in organello systems capable of the massive net synthesis of
Pchlide a from exogenous ALA and tetrapyrrole substrates (Daniell and Rebeiz
1982a , b ; Mattheis and Rebeiz 1977a , b ;Rebeizetal. 1975 ; Tripathy and Rebeiz
1986 ), and the development of sensitive analytical fluorescence methodologies that
allowed the demonstration of the DV and MV heterogeneity of the metabolic pools
between Mg-Proto and Chl a (Rebeiz et al. 2003 ). With the use of similar techniques,
the reactions between Mpe and Pchlide a have been reinvestigated by Castelfranco
and collaborators (Walker et al. 1988 ; Wong and Castelfranco 1985 ). In a series of
experiments involving the conversion of the added putative tetrapyrrole intermediates
Search WWH ::




Custom Search