The B12Vitamins and Methionine in the Metabolism of Prymnesium parvum

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Abstract
SUMMARY Methionine or ethionine, although capable of serving as sole nitrogen source for Prymnesium parvum, cannot replace or spare the vitamin B12 nutrient requirement for the growth of this flagellate. In the presence of vitamin B12 methionine counteracted the inhibition of growth exerted by some vitamin B12 analogues which are substituted at the benzimidazole part of the molecule. No such effect was observed against the inhibition by certain other analogues. Analogue FIII (α-(5-hydroxybenzimidazolyl)-cobamide cyanide) replaced vitamin B12 in the presence of methionine, and to a lesser degree also in the presence of other methyl donors such as methylmethionine sulphonium iodide, dimethylpropiothetin, choline chloride and betaine. The conclusion drawn is that for P. parvum analogue FIII is capable of replacing vitamin B12 in all the metabolic pathways other than methyl-group synthesis. For the latter process, the benzimidazole methyl groups present in vitamin B12 and analogue FIIIm (α-(5-methoxy-benzimidazolyl)-cobamide cyanide) are indispensable.