888 7. MERCURIALS 



Pseudomonas aeruginosa by DeTurk and Bernheim (1960), the induction 

 of enzymes for the oxidation of putrescine, benzoate, and }^-aminobutyrate 

 being reduced 50% by 0.0028 mM p-MB. The enzymes themselves are not 

 inhibited at this concentration. Partial protection by Fe++ when it is added 

 with the mercurial or shortly after was observed. It is now known that 

 enzyme induction is not a valid system for estimating the effects of in- 

 hibitors on protein synthesis in general, because there are many other fac- 

 tors involved. In the inhibition cited, it was in fact postulated that some 

 transport process in the membrane requires Fe++ and that this is the site 

 of attack by the mercurial. 



Porphyrin Synthesis 



The formation of porphyrins from glycine and a-ketoglutarate by Rhodo- 

 pseudomonas spheroides is completely blocked by 0.04 mM p-MB, and from 

 aminolevulinate by 0.1 mM (possibly by lower concentrations since they 

 were not tested) (Lascelles, 1956). The formation of aminolevulinate from 

 glycine, phosphoenolpyruvate, and succinyl-CoA is completely prevented 

 by 0.44 mM p-MB (Gibson et al., 1958). It would thus appear that steps 

 both pre- and post-aminolevulinate are vulnerable. The report of Granick 

 (1958) that 1 mM p-MB does not interfere with protoporphyrin synthesis 

 from glycine and or-ketoglutarate in chicken erythrocytes is surprising, but 

 may be attributed to the high density of the cell suspension (around 45% 

 by volume) and the consequent binding of the mercurial to nonenzyme 

 proteins. The condensation of porphobilinogen to uroporphyrinogen is al- 

 most totally blocked by 0.02 mM Hg++ and 0.1 mM p-MB (Lockwood 

 and Benson, 1960), and the subsequent conversion of uroporphyrinogen to 

 coproporphyrinogen is again essentially blocked by 0.012 mM Hg++ and 

 0.7 mM p-MB (Mauzerall and Granick, 1958), if the results on the isolated 

 enzymes catalyzing these reactions can be applied to cellular preparations. 

 The incorporation of Fe++ into protoporphyrin to form heme is not so sen- 

 sitive, in chicken erythrocyte hemolyzate being inhibited 64% and 58% 

 by 1 mM Hg++ and p-MB, respectively (Kagawa et al., 1959). The purified 

 chelating enzyme from rat liver is inhibited 75% by 0.1 mM Hg++ (Labbe 

 and Hubbard, 1961), the greater effect probably being due to the relative 

 purity of the preparation. Again one can speculate that a depression of 

 porphyrin synthesis may be of some significance in growth studies or 

 chronic poisoning. 



Biolumlnescence 



One of the very few thorough, quantitative, and interesting investiga- 

 tions on mercurial inhibition was made by Houck (1942), who studied the 

 effects of Hg++ on the luminescence of Achromobacter fischeri. The standard 

 conditions were as follows: pH 7.3, temperature 25°, 25 mM glucose as 



