Premium
Two forms of N intermediate (N open and N closed ) in the bacteriorhodopsin photocycle
Author(s) -
Radionov Alexey N,
Kaulen Andrey D
Publication year - 1999
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(99)00577-3
Subject(s) - azide , bacteriorhodopsin , chemistry , protonation , halobacteriaceae , microsecond , isomerization , photoprotein , ion , open shell , crystallography , photochemistry , stereochemistry , catalysis , membrane , biochemistry , physics , bioluminescence , organic chemistry , halobacterium salinarum , astronomy
Glutaraldehyde, aluminum ions and glycerol (that inhibit the M intermediate decay in the wild‐type bacteriorhodopsin and azide‐induced M decay in the D96N mutant by stabilization of the M closed ) accelerate the N decay in the D96N mutant. The aluminum ions, the most potent activator of the N decay, induce a blue shift of the N difference spectrum by ∽10 nm. Protonated azide as well as acetate and formate inhibit the N decay in both the D96N mutant and the wild‐type protein. It is concluded that the N intermediate represents, in fact, an equilibrium mixture of the two (‘open’ and ‘closed’) forms. These two forms, like M closed and M open , come to an equilibrium in the microseconds range. The absorption spectrum of the N open is slightly shifted to red in comparison to that of the N closed . Again, this resembles the M forms. 13‐ cis ‐all‐ trans re‐isomerization is assumed to occur in the N closed form only. Binding of 1–2 molecules of protonated azide stabilizes the N open form. Existence of the ‘open’ and ‘closed’ forms of the M and N intermediates provides the appropriate explanation of the cooperative phenomenon as well as some other effects on the bacteriorhodopsin photocycle. Summarizing the available data, we suggest that M open is identical to the M N form, whereas M 1 and M 2 are different substates of M closed .