Inhibition of Glycine Decarboxylation and Serine Formation in Tobacco by Glycine Hydroxamate and Its Effect on Photorespiratory Carbon Flow

Abstract

Glycine hydroxamate is a competitive inhibitor of glycine decarboxylation and serine formation (referred to as glycine decarboxylase activity) in particulate preparations obtained from both callus and leaf tissue of tobacco [cv. John Williams Broad leaf]. In preparations from tobacco callus tissues, the Ki for glycine hydroxamate was 0.24 .+-. 0.03 mM and the Km for glycine was 5.0 .+-. 0.5 mM. The inhibitor was chemically stable during assays of glycine decarboxylase activity, but reacted strongly when incubated with glyoxylate. Glycine hydroxamate blocked the conversion of glycine to serine and CO2 in vivo when callus tissue incorporated and metabolized [1-14C]glycine, [1-14C]glycolate, or [1-14C]glyoxylate. The hydroxamate had no effect on glyoxylate aminotransferase activities in vivo, and the nonenzymic reaction between glycine hydroxamate and glyoxylate did not affect the flow of carbon in the glycolate pathway in vivo. Glycine hydroxamate is the first known reversible inhibitor of the photorespiratory conversion of glycine to serine and CO2.