Glycine transport in human diploid fibroblasts was shown to be by a single sodium-dependent system. Glycine transport does not appear to exhibit transstimulation or transinhibition. Transport appears to be similar to the A transport system of other mammalian cell lines, as defined by competition patterns. Normal and nonketotic hyperglycinemia (NKH) fibroblasts could not be distinguished on the basis of accumulation or initial rates. A distribution ratio of 15 to 30 was reached by both types of cells. The normal lines have slightly lower apparent Kms (1.1–1.3 mM) than the NKH lines (1.8 to 2.4 mM). The values for the Vmax of the normal cells (11.4–12.9 nmole/mg/min) and the NKH cells (7.0–16.7 nmole/mg/min) overlapped. There were no measurable differences in either the long-term incorporation into protein of leucine and glycine or the oxidation of glycine in normal and NKH fibroblasts.Speculation
In the cell lines used in this study, it does not appear that nonketotic hyperglycinemic fibroblasts contain a glycine transport defect. NKH cells could not be reliably distinguished from normals using transport, incorporation into proteins, or oxidation of glycine.