EFFECTS ON ALGAE AND PROTOZOA 



573 



quinone with SH groups and the mechanism by which it inhibits the 

 pyruvate decarboxylase. Other attempted correlations with enzyme in- 

 hibition, as with amylase, catalase, or polyphenol oxidase (Owens, 1953 a, 

 b) are invalidated by many exceptions; e. g., menadione inhibits fungal 

 growth rather potently but has no effect on amylase, and toluquinone is 

 less than 1/2000 as inhibitory to growth as 2,3- dichloro-l,4-napthoquinone 

 but inhibits amylase more potently. One disturbing note is the fact that 

 3,4-dichlorotoluene is a moderately potent inhibitor of fungal growth, 

 indicating that more work should be done on chlorinated nonquinonoid 

 compounds. 



EFFECTS ON ALGAE AND PROTOZOA 



Algae are perhaps the most sensitive to the quinones of all organisms, 

 on the basis of the limited data available. 2,3-Dichloro-l,4-naphthoquinone 

 is much more potent than any other substance tested on blue-green algae, 

 being inhibitory to growth at 0.00001 mM, at which concentration no effect 

 on other aquatic life was noted (Fitzgerald et al., 1952). The growth of 

 Euglena gracilis is also potently inhibited by naphthoquinones, but there 

 is often quite marked variation in sensitivity between the normal green 

 form and a white chlorophyll-free form (obtained by treatment with strepto- 

 mycin) (Table 5-11) (Schopfer and Keller, 1951). The marked differences 

 in the susceptibility ratio for the different quinones points to more than a 

 single mechanism of action. Furthermore, menadione inhibits the white 

 form more potently in the light than in the dark, while the green form is 

 inhibited about equally in light and dark. Nicotinate is a growth inhibitor 

 and adds to the menadione inhibition in the green form, but antagonizes 

 the menadione inhibition in the white form. Of course, the different sus- 

 ceptibilities need not depend on the presence or absence of chlorophyll, 

 but may be related to other simultaneous metabolic changes; nevertheless, 



