The Relation of Optical Form to the Utilization of Amino Acids. I. Utilization of Stereoisomeric Forms of Glutamic Acid by Carrot Root Disks

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Abstract
L-glutamate was absorbed, by carrot root disks (Daucus carota var. chatenay). at a much faster rate than the D-enantiomorph. Differences in the degree of absorption of the two isomers may be the result of differences in their rates of penetration into the cells. It may be suggested that the amino acid first combines with some cellular constituent at the surface and this complex is transferred into the cell. Since the cell membrane consists of optically active material, differences in penetrability of stereoisomers might be possible. Carrot root cells showed a marked ability to utilize L-glutamate, especially when supplied in combination with ammonium sulphate. On the other hand, there was no convincing evidence of the utilization of the D-glutamate absorbed, which seemed to accumulate in the cells. An interesting observation was the depressing effect of D-glutamate on the uptake and utilization of ammonium-N. Addition of D-glutamate to L-glutamate in the external medium neutralized the stimulating effect L-glutamate on the uptake and utilization of ammonium-N.