SHMT1 and cancer: In contrast to cancer cell lines, infusion of [13C2] glycine in adult humans indicated that glycine can contribute to serine synthesis via the “reverse” SHMT-mediated reaction, not only directly (as an intact molecule) but also as a 1C donor (via 5,10-methylene THF) following glycine cleavage (Kalhan and Hanson, 2012, Lamers et al., 2007, Lamers et al., 2009).