itation ▁peak ▁around ▁ 3 7 0   nm ▁( U V - A ▁light ). ▁The ▁main ▁emission ▁peak ▁is ▁at ▁appro x . ▁ 4 9 5   nm , ▁with ▁a ▁shoulder ▁around ▁ 5 2 0   nm . ▁One ▁variant ▁of ▁P p 2 F b FP ▁( Q 1 1 6 V ) ▁exhib its ▁a ▁ 1 0   nm ▁blue ▁shift ▁in ▁both ▁the ▁exc itation ▁and ▁emission ▁spect ra . ▁ ▁Phot oph ys ical ▁properties ▁ ▁The ▁phot oph ys ical ▁properties ▁of ▁the ▁F b FP s ▁are ▁determined ▁by ▁the ▁chrom oph ore ▁itself ▁and ▁its ▁chemical ▁surrounding ▁in ▁the ▁protein . ▁The ▁ext inction ▁coefficient ▁( ε ) ▁is ▁around ▁ 1 4 . 2 0 0 ▁M − 1 cm − 1 ▁at ▁ 4 5 0   nm ▁for ▁all ▁described ▁F b FP s , ▁which ▁is ▁slightly ▁higher ▁than ▁that ▁of ▁free ▁FM N ▁( ε ▁= ▁ 1 2 . 2 0 0 ▁M − 1 cm − 1 ▁). ▁The ▁Fl u ores c ence - Quant um ▁yield ▁( Φ ) ▁var ies ▁significantly ▁between ▁different ▁F b FP s ▁and ▁ranges ▁from ▁ 0 . 2 ▁( phi LO V 2 . 1 ) ▁to ▁ 0 . 4 4 ▁( E c F b FP ▁and ▁i LO V ). ▁This ▁represents ▁an ▁almost ▁two fold ▁increase ▁compared ▁to ▁free ▁FM N ▁( Φ ▁= ▁ 0 . 2 5 ).