Table 4. ZINDO Absorption Energy Calculations.

	Exp.	Proteina	Chromophoreb	Cluster 1c	Cluster 2d
mKateS158A	2.11 (588)	2.36 (526)	2.14	2.30	2.20
GmKatepH10	2.07 (598)	2.31 (536)	2.14	2.30	2.16
GmKatepH7	2.79 (445)	3.06 (405)	3.04	3.07	3.02

Energies are given in eV, wavelengths in nm in parentheses. All geometries were optimized within the protein environment using a QM/MM DFT approach.

^a. Cluster including the chromophore, R⁹², S/C¹⁴³, R¹⁹⁷, E²¹⁵, Wat1, and Wat4.

^b. Anionic in mKate^S158A and GmKate^pH10, neutral in GmKate^pH7.

^c. Cluster 1 includes the chromophore, R⁹², R¹⁹⁷, E²¹⁵, and Wat4.

^d. Cluster 2 includes the chromophore, S/C¹⁴³, and Wat1.