Role of 5'-deoxy-5'-methylthioadenosine in growth of several microbial B12 requirers

5'-Deoxy-5'-Methylthioadenosine (MTA) figures in cellular methionine and polyamine syntheses. It replaces B12 for growth of the chrysomonad protozoan Poteriochromonas malhamensis at a ratio of MTA:B12 of approximatly 10,000,000:1 (by weight). MTA does not replace B12 for other B12-requirers, e.g.: Euglena gracilis, Lactobacillus leichmannii, and Escherichia coli 113-3. The methionine synergism for P. malhamensis growth is also negated when B12 activity is annulled by alkali treatment; MTA is not inactivated by such treatment. The growth promoting activity of various deoxynucloesides and deoxynucloetides for P. malhamensis and other B12-requirers is reported here due to contamination by cobalamins. Ethionine antagonizes the growth-enhancing effect of MTA, methionine, and B12, individually and collectively -evidence that MTA plays a role in supplying methionine for P. malhamensis growth. MTA concentrations in body fluids and mammalian tissues are too low to interfere with the use of P. malhamensis for estimating only metabolically active B12.