SIDNEY F. VELICK 



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300 340 380 420 

 Emission, myu 



Fig. 9. Huorescence emission l)ands of LDH, GPD, and free tryptophan excited 

 at 280 m/i from solutions of the same optical density at 280 ni/x. The areas under 

 the emission bands, under these conditions, are proportional to the respective 

 fluorescence quantum yields. 



On the other hand the quantum yield of the LDH emission is high, 

 nearly 40 instead ot the 10 per cent shown by GPD. If we assume 

 that only light absorbed directly in the tryptophan of LDH is re- 

 emitted as fluorescent light, then the quantimi yield of the tryptophan 

 emission is of the order of 70 per cent. Since the tryptophan in the 

 protein is in a protected environment, a high quantum yield intro- 

 duces no serious problem. That the high yield of tryptophan emis- 

 sion in LDH is a result of the special tertiary structure of the pro- 

 tein is shown in Fig. 10. The LDH is strongly quenched in 6 M urea, 

 whereas free tryptophan is significantly enhanced. 



