478 L. BOGORAD 



uroporphyrins were not decarboxylated upon incubation with frozen 

 and thawed Chlorella preparations of the same kind used in the 

 experiments described above (9,10). These observations are sum- 

 marized in Fig. 2. 



By way of further inquiry into this matter, Chlorella preparations 

 have been incubated with uroporphyrinogens prepared by reducing 

 the methene bridges of uroporphyrins with hydrogen, using a pal- 

 ladium catalyst. Small amounts of porphyrins with fewer than eight 

 carboxyl groups per molecule have been recovered, but such ex- 

 periments have not provided satisfactory quantitative evidence that 

 the bulk of the uroporphyrinogens obtained by this reduction of 

 uroporphyrins are identical with the colorless product of the action 

 of PBG deaminase on PBG. 



^^ Uroporphyrin! 



PBG PBC DMminqse — _> colorless " spin, enz. , uroporphyrin! 

 NH<^ product - 



3 



A 



Porphyrins with 



fewer than 6 



-COOH groups 



Fig. 2. 



The arrangement of the acetic and propionic acid side chains pre- 

 cludes a tetrapyrrolic precursor of uroporphyrin I as a precursor of 

 protoporphyrin IX or chlorophyll. An enzyme has recently been par- 

 tially purified from wheat germ which plays a role in the biosynthesis 

 of an octacarboxylic tetrapyrrolic precursor of uroporphyrin III; 

 such a compound may be considered the most likely initial tetrapyr- 

 role in this biosynthesis chain. 



One fraction prepared from ac^ueous extracts of wheat germ by 

 ammonium sulfate fractionation catalyzes the consumption of PBG; 

 uroporphyrin III has been recovered from the reaction mixture and 

 characterized by paper chromatography. (Both uroporphyrins III and 

 I have been recovered after PBG has been incubated with some 

 preparations of this fraction.) It is of considerable interest that if such 

 l)reparations are aged in the refrigerator for 2 days or are heated at 

 55°C'. for 15 minutes, the capacity for the consumption of PBG 

 appears to be unaltered but only uroporphyrin I is produced. (It 



