Bacteriorhodopsin is a protein used by by halo bacteria that lives in highly salt conditions , it captures light energy and uses it to ATP synthesis rather metabolizing substrates.

1. SHRUTHI SHREE GANDHI.S
I MSC BIOCHEMISTRY
SRI RAMAKRISHNA COLLEGE OF ARTS AND
SCIENCE FOR WOMEN.
TRANSPORT PROCESS DRIVEN BY LIGHT
BACTERIORHODOPSIN

2. TRANSPORT PROCESS DRIVEN BY
LIGHT
● Light energy can be used by micro organisms like halobacterium salinarium
, To synthesize ATP without metabolizing any substrates.
● halobacterium salinarium lives in highly salt conditions. hence they are
totaly dependant on ATP production without utilizing any substrates with
the help of protein called bacteriorhodopsin on their cell membrane.
● The light energy can be utilized by driving an uphill transport process
across the cell membrane.

3. drawing
Appearance of lake or ocean in purple color
containing halobacterium salenarium due to
absorption of uv light
Halobacterium salinarum

4. Bacteriorhodopsin
● Bacteriorhodopsin is a light driven photon pump present in cell
membrane of certain species of photosynthetic bacteria like
halobacterium salinarum.
● Bacteriorhodopsin a protein made of 7 membrane spanning alpha
helices of single polypeptide chain .
● with retinal molecule present in the center or buried inside and are
connected through the lysine residue.

5. Structure of bacteriorhodopsin
The author of the work,the original authors of the Protein Data Bank
(PDB) structural dataand the molecular graphics program used [CC
BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

6. MECHANISM OF ATP
PRODUCTION
● When light falls on bacteriorhodopsin protein, protons are pumped out.
● It is caused due to the retinal chromophore which photo isomerizes from
trans retinal to cis-retinal resulting in the release of proton.
● Thus a photo cycle of conformational changes occur from cis to trans ,
resulting in the release of gradient of protons across the cell membrane.
● and the released protons from retinal molecule are compensated by
protons from cytoplasm.

7. Cont…
● The resultant proton gradient present on the extracellular surface
enters cytoplasm through ATPase present on the cell membrane.
● where they are utilized by the enzyme ATPase to synthesize ATP.Thus
the bacteria synthesizes ATP without metabolizing any substrates.
● When light fall on halo rhodopsin , another pigment protein present
on the bacterial membrane, it facilitate the diffusion of chloride ions
present on extracellular surface to move from region of higher
concentration in to the ( cytoplasm)region of lower concentration
through halo rhodopsin.

8. Cont…
● The chloride ions after entering the cytoplasm now involve in
the electrostatic attraction of positively charged hydrogen ions
on the extracellular surface, thus pulling hydrogen ions in to
the cytoplasm via ATPase.

9. Transport process

10. MECHANISM OF RELEASE OF H+
● When light falls on bacteriorhodopsin protein, the retinal chromophore photo
isomerizes by changing its conformation from trans- retinal to cis-retinal.

11. The release of protons
1) due to photoisomerisation,
the position of positively charged
cis-retinal molecule is now near
the negatively charged aspartate
85 which is found closer to
extracellular surface.
1) cis retinal molecule on excited state
now releases an proton from the
nitrogen atom of the amide group
1) due to the electrostatic attraction
between the negatively charged
oxygen on the aspartate 85.

12. Cont…
4) now cis retinal becomes
negatively charged
molecule.
While the aspartate 85
becomes positively
Charged by acquiring a
proton.

13. Cont…
5) The aspartate 85 molecule
tranfers the proton
To the extra cellular space via a
water molecule and again becomes
negatively charged.
Which induces the aspartate85
molecule to gain proton again from
the cis retinal molecule.

14. Cont…
6)The cis retinal molecule after
losing a proton and becomes
negatively charged,acquires a
proton from aspartate 96
present on the other side and
near cytoplasm .
The cis retinal molecule enters
ground state after acquiring a
proton from aspartate 96.

15. Cont..
7)The aspartate 96
molecule gains its lost
proton by acquiring a
proton from the
cytoplasm.
Thus,the cycle continues
When the retinal protein
absorbs light
And isomerises resulting
in pumping of protons..

16. ●Thank you