Inhibition of Glycolipid Biosynthesis in Chloroplasts by Ozone and Sulfhydryl Reagents

Abstract

The metabolism of uridine 5'-pyrophosphate-galactose by spinach (Spinacia oleracea) chloroplast preparations was inhibited by ozone. The formation of digalactosyl diglyceride and trigalactosyl diglyceride was inhibited much more than the formation of monogalactosyl diglyceride, steryl glycoside, and acylated steryl glycoside. Essentially identical results were obtained when glycolipid synthesis was inhibited by N-ethyl maleimide, p-hydroxymercuribenzoate, and CdCl(2). Iodoacetate and iodoacetamide affected neither the total incorporation of sugar from uridine 5'-pyrophosphate-galactose nor distribution of the incorporated sugar in the various glycolipids.Ozone reacted with model membrane systems prepared with egg lecithin. In the absence of reduced glutathione, products included malonaldehyde and hydrogen peroxide. In the presence of glutathione, malonaldehyde was still produced, but the glutathione was oxidized and no peroxide was detected. When these studies were extended to chloroplast preparations, it was also found that malonaldehyde was produced and glutathione was oxidized.It was concluded that ozone inhibits glycolipid biosynthesis in chloroplast preparations by way of oxidation of enzyme sulfhydryl groups but that this reaction may be a secondary effect of oxidation of unsaturated fatty acids.