640 



LIGHT AND LIFE 



0.09 



0.08 



0.07 



I- 



0.06 



0.05 



liJ 

 Q 



< 0.04 

 U 



I- 

 d. 

 O 0.03 



0.02 - 



0.01 - 



0.00 



PPNR-SPEC. ACTIVITY = 75 

 CONC. = 76.5 x/ML. 



I 



PPNR - SPEC. ACTIVITY ^ 75 

 CONC. = I 5 3 y/ M L . 



260 280 300 320 340 320 360 400 440 480 520 560 



WAVE LENGTH 



Fig. 3. .Absorption spectrum of purified photosynthetic pyridine nucleotide 



reductase. 



amino acid residues (excluding the tryptophan content of the enzyme) 

 and there does not appear to be any methionine in the enzyme. 

 The minimum molecular weight calculated from amino acid analysis 

 is about 12,000, but this value does not include the contribution of 

 tryptophan. 



Under acid conditions, the enzyme is irreversibly bleached and the 

 activity is completely lost. The bleaching of the enzyine is accom- 

 panied by a loss of, at least, the absorption at 420 and 460 m/x. A 

 similar loss in absorption in this region is observed under alkaline 

 conditions. 



Relation to Methaemoglobin-reducing Factor 



Davenport and Hill (9) have recently reported the purification 

 of a protein factor from leaves which was shown previously (10) to 

 catalyze the reduction of nicthaemoglobin and metmyoglobin by il- 

 luminated chloroplasts. They have named this protein the "methaem- 

 oglobin-reducing factor." In addition to the compoinids indicated 

 above, this factor catalyzes the reduction of a number of haem-protein 

 compounds, including cytochrome c, ])y illuminated chloroplasts. 



