Methylthioadenosine serves as a single carbon source to the folate co-enzyme pool in rat bone marrow cells

ribose-U-14C]Methylthioadenosine (MTA) was prepared by incubating methionine with 14C-U]ATP in the presence of methionine adenosyltransferase and the resulting S-adenosylmethionine was heated to release MTA. Labelled 14C]MTA, when incubated with rat bone marrow cells, yielded 14C]formate which was used in the synthesis of adenine and guanine. Unlike 14C from sodium, formate, serine and glycine, there was no decline in 14C utilization from MTA with bone marrow cells from rats in which cobalamin had been inactivated by exposure to nitrous oxide. It was concluded that methionine via MTA is a significant contributor of single-carbon units at the formate level of oxidation and that this pathway is maintained in cobalamin 'deficiency'.