VARIOUS METABOLIC PATHWAYS 697 



role in CO2 fixation in Chlorella is decreased by exposure to arsenite, as 

 well as to other SH reagents. Since ribulose-diP carboxylase is not sensitive 

 to arsenite, possibly arsenite interferes with the generation of ribulose-diP, 

 but the action is not on the ribulose-5-P kinase. In contrast to the evolution 

 of oxygen, the photoproduction of hydrogen by Rhodospirillum rubrum 

 is quite sensitive to arsenite and it was suggested that vicinal SH groups 

 occur on the enzyme system (Gest et al., 1962). On the other hand, the 

 nonphotochemical evolution of hydrogen by rumen microorganisms is 

 inhibited poorly by arsenite (Peel, 1960), and the utilization of hydrogen 

 for reductive and energy-supplying purposes in E, coli (Lascelles and Still, 

 1947) and Hydrogenomonas facilis (McFadden and Atkinson, 1957) is 

 scarcely affected by arsenite. 



Miscellaneous Metabolic Pathways 



A few actions of arsenite on certain important metabolic systems will 

 be mentioned only briefly because insufficient work has been done on the 

 mechanisms involved. Luminescence of Achromohacter fischeri was shown 

 to be dimmed by 3 n\M arsenite and almost abolished by 4 mM arsenite 

 (Korr, 1935), which indicates rather low sensitivity, but more recently 

 it has been claimed that arsenite strongly inhibits the luminescence, although 

 no concentrations were given (Rogers and McElroy, 1958). Sulfur oxidation 

 by Thiohacillus thiooxidans is moderately inhibited by arsenite (28-42% 

 by 1 mM), respiration being affected less and CO., fixation more (Vogler 

 et al., 1942; Iwatsuka et al, 1962). The growth of these bacteria is stopped, 

 however, at concentrations without effect on sulfur oxidation. The synthesis 

 of riboflavin in the epicotyls of lupine seedlings is depressed at very low 

 arsenite concentrations, the level of riboflavin falling 24% in the presence 

 of 0.0001 mM arsenite, but as the concentration of arsenite is increased 

 another action must appear because around 0.01 mM there is essentially 

 no effect and at 0.03 mM there is an elevation of the riboflavin level (Gus- 

 tafson, 1955). The deiodination of thyroxine in an extract of rat liver is 

 unaffected by 1 mM arsenite (Maclagan and Reid, 1957). The metabolism 

 of ethanol in rabbits is unaltered by toxic doses of arsenite, as measured 

 by blood ethanol levels following slow intravenous infusions (Hulpieu et 

 al, 1948). Regrettably little is known about the effects of the arsenicals 

 on the synthesis of nucleotides and nucleic acids, but Skipper et al. (1951) 

 reported that 9 mg/kg potassium arsenite injected into mice given formate- 

 C^* quite markedly reduces visceral purines (52%) and nucleic acids (61%). 

 Such an effect must certainly be of significance in producing the pattern 

 of arsenite poisoning and the growth inhibitions observed. Certain other 

 metabolic actions will be taken up in connection with functional or growth 

 disturbances. 



