628 



F. Dickens 



in the reduced form (TPNH) in all fractions. This implies independent opera- 

 tion of the two types of pyridine nucleotide systems, presumably by spatial or 

 enzymic considerations. 



Table 1. Intracellular distribution of pyridine 



NUCLEOTIDES IN RAT LIVER (/ig/g Liver) 



After the soluble fraction, which has the highest percentage of the total 

 DPN (75 %) and of total TPN (45 %), the next highest proportion of pyridine 

 nucleotide is in the mitochondria (13% of total DPN, 36% of total TPN, 

 mainly as TPNH). It is noteworthy that there is actually more TPN than 

 DPN in liver mitochondria. Washing the mitochondria by suspension in 

 isotonic sucrose containing nicotinamide and recentrifugation using the 

 'layering' technique, did not remove much pyridine nucleotide although some 

 oxidation of reduced forms occurred after two such washings (Table 2 (a)). 

 On the other hand, two similar washings of the nuclei resulted in a rather 

 considerable fall of oxidized and reduced DPN and TPN which presumably 

 diffuse slowly from the nuclei. 



Table 2. (a) Effect of washing rat liver mitochondria (0°C) on their content 



OF PYRIDINE nucleotides (GlOCK AND McLeAN, 1956) AND (b) RELEASE OF 

 BOUND DPN AND TPN BY SHORT AEROBIC INCUBATION (30°C) WITH PHOSPHATE 



OR ADP (Purvis, 1958a) 



(AU values in //moles/g mitochondrial protein.) 



