SIDNEY SHItRJN AND NATHAN O. KAPLAN 



151 



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300 



340 



380 



420 



WAVELENGTH (m^) 



Fig. 7. Spectral changes of thionicotinamide DPNH after illumination. Curve 

 A, absorption spectrum of 9.3 X '^"^ '^^ thionicotinamide-DPNH in O.I M phos- 

 phate buffer, pH 9.2. Curve B, absorption spectrum of same concentration of re- 

 duced analogue after a 5-minute exposure to the infrared source of the Cary re- 

 cording spectrophotometer kept at 400 m^u. 



metals, a formation accompanied by distinct color changes (15) . The 

 addition of equimolar amounts of p-chloromercuribenzoate to solu- 

 tions of thionicotinamide-DPNH resulted in an intensification of the 

 yellow color of the analogue and a shift of the absorption maximum 

 toward the red. The rate of bleaching of the complex was only 

 one-tenth that observed with the untreated coenzyme analogue. 



Almost all known enolizablc thiocarbonyl groups are alkylated in 

 such a way as to suggest that the molecule exists in large part as the 

 thiol form. When the thionicotinamide analogue of DPNH was 

 treated with dimethyl sulfate in sodiinn bicarbonate buffer, at pH 



