Biology Reference
In-Depth Information
Fig. 16.3 Schematics of a linear model of a PSU in the unfolded state (Reproduced from von
Wettstein et al. 1995 )
As mentioned in Chap. 15 , we have recently examined three possible models for that
scenario, which have been referred to as: (a) the single-branched Chl biosynthetic
pathway (SBP)-single location model, (b) the SBP-multilocation model, and (c) the
multi-branched Chl biosynthetic pathway (MBP)-sublocation model. The models
take into account the dimension of the PSU (Bassi et al. 1990 ), the biochemical
heterogeneity of the Chl biosynthetic pathway (Rebeiz et al. 1994 , 2003a ) and the
biosynthetic and structural complexity of the thylakoid and the Chl.
Assembly of Chl-Protein Complexes: The SBP-Single Location Model
The SBP-single location model is depicted schematically below, in Fig. 16.4 , which
has been reproduced from Fig. 15.1 . As mentioned previously, within the PSU, this
model accommodates only one Chl-apoprotein biosynthesis center and no
Chl-apoprotein biosynthesis subcenters. Within the Chl-apoprotein biosynthesis
center, Chl a and b are formed via a single-branched Chl biosynthetic pathway
(Fig. 16.2 ) at a location accessible to all Chl-binding apoproteins. The latter will
have to access that location in the unfolded state, pick up a complement of MV
Chl a and/or MV Chl b , and undergo appropriate folding. Then the folded
Chl-apoprotein complex has to move from the central location to a specific PSI,
PSII, or Chl a/b LHC-protein location within the Chl-apoprotein biosynthesis
center over distances of up to 225 ˚ (Kolossov et al. 2003 ; Kopetz et al. 2004 ).
In this model, it is unlikely to observe resonance energy transfer between metabolic
tetrapyrroles and some of the Chl-apoprotein complexes located at distances longer
than 100 ˚ . This is because resonance excitation energy transfer takes place only
over distances shorter than 100 ˚ (Calvert and Pitts 1967 ).
Search WWH ::




Custom Search