Glycine Transport by Human Diploid Fibroblasts—Absence of a Defect in Cells from Patients with Nonketotic Hyperglycinemia

Abstract

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.