SUMMARY: The formation of chlorophyll in non-proliferating etiolated cells of var. is inhibited by some antimetabolite analogues of vitamins. The cell size and cell mass of light-grown euglenas is considerably increased in vitamin B 12 deficiency. The inhibitory effect of 2,6-diaminopurine on chlorophyll formation in non-proliferating euglenas was not annulled by vitamin B 12; 6-mercaptopurine, sulphanilamide and benzimidazole were without effect. Isoniazide inhibition is not reversed by niacin: surprisingly, the vitamin itself is markedly inhibitory. The inhibitory effect of niacin, however, is prevented by pyridine-3-sulphonate. Niacin and its analogues were more inhibitory to growth in the dark than in the light. The inhibition of growth by niacin in the light is annulled appreciably by either glucose or pyruvate, or an overwhelming concentration of vitamin B 12. Aminopterin, desoxypyridoxine and 2-chloro--aminobenzoic acid do not have any effect on chlorophyll synthesis in non-proliferating euglenas; the last mentioned inhibits the growth of the alga more in the dark than in the light. Thiamine deficiency inhibits growth; such sub-optimally grown euglenas also synthesize less chlorophyll per cell on subsequent illumination under non-proliferation conditions.

The negative growth response of light-grown var. to niacin suggests a microbiological method of estimating this vitamin in biological materials and pharmaceutical preparations up to concentrations of 70 μg./ml. in the growth medium. The 50% inhibition level of niacin in the light is 46 μg./ml.


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