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TitleLight-harvesting and the Primary Photochemistry of Roseiflexus castenholzii
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                            Washington University in St. Louis
Washington University Open Scholarship
	January 2010
Light-harvesting and the Primary Photochemistry of Roseiflexus castenholzii
	Aaron Collins
		Recommended Citation
Microsoft Word - Dissertation with appendix.doc
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Page 1

Washington University in St. Louis
Washington University Open Scholarship

All Theses and Dissertations (ETDs)

January 2010

Light-harvesting and the Primary Photochemistry
of Roseiflexus castenholzii
Aaron Collins

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Department of Chemistry 

Dissertation Examination Committee: 

Robert E. Blankenship, Chair 
Dewey Holten  
Robert G. Kranz 
Joshua A. Maurer 
Liviu M. Mirica 
Yinjie J.Tang 




Aaron Michael Collins 

A dissertation presented to the 
Graduate School of Arts and Sciences 

of Washington University in 
partial fulfillment of the 

requirements for the degree 
of Doctor of Philosophy 


August 2010 

Saint Louis, Missouri

Page 74


EM images of the LH-only revealed some circular and elliptical particles with

most lacking density in the center, confirming the lack of the RC (figure 3.6B, green

box). The dimensions of closed rings observed for the LH-only were approximately the

same as the LHRC. There appeared to be many fewer side projections and many of the

rings were not complete (figure 3.6 red box).

In total, several thousand single projections were boxed (figure 3.6B and C) and

used to create image classes that are the average of several hundred particles. Three

projections for each the LHRC and the LH-Only are shown in figure 3.7. Of these

classes of particles, three projections assumed; 1- a bottom projection looking down

into the periplasmic side of the complex, 2 – a top projection looking down into the

cytoplasmic side of the complex and 3 – a side view, presumably in the plane of the

ring. Most obvious of these projections were the side views (figure 3.7C and F). The C-

subunit is well established in the side view of the LHRC and extends perpendicular to

the plane of the ring structure. The top and bottom projections are ambiguous to

determine but reveal that the circular or elliptical structure is a closed ring. The LHRC

from R. castenholzii lacks the H-subunit found in all purple bacteria but maintains a

large C-subunit. One side of the complex should most likely have a protrusion

representing the C-subunit while the opposite side could be relatively flat. The C-

subunit might be responsible for the weak staining that is observed in the center of the

complex that extends to the edge of the ring (figure 3.7D). If this is indeed the C-

subunit protrusion, it is interesting that it is observed to orient along the short axis of

the elliptical ring.

Page 75



The study of photosynthetic membrane complexes among FAPs has been

largely limited to C. aurantiacus due to its relative ease to grow and lack of other

species that can be cultured in high yield. However, C. aurantiacus contains

chlorosomes that often dominate the optical properties of samples. Despite this,

procedures have been developed to prepare cytoplasmic membranes devoid of

chlorosomes (Feick et al. 1982). The discovery and isolation of R. castenholzii by

Hanada et al provides an opportunity to study a representative member of the FAPs

without chlorosomes (Hanada et al. 2002). Here we present a full description of the

purification of a full complement of photosynthetic complexes from R. castenholzii: the

RC, LH-only, and the LHRC.

The fluorescence lifetime measurements of the LHRC are consistent with a

nearly uniform decay of antenna excitation by RC trapping. Several different excitation

were used to directly excite various electronic bands of the LHRC and LH-only. All of

the difference excitations produced essentially the same emission kinetics and probably

reflects a rapid decay of excitation to the lowest excited energy level, S1, of B880.

When the RC is not present in the sample, then the lifetime of the B880 antenna

pigments is considerably longer and decays monoexponentially in about 900 ps.

Model of the LH antenna in R. castenholzii

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