Carbon isotope ratios of amylose, amylopectin and mutant starches

Abstract Carbon isotope ratios (expressed as δ 13 C values) were determined for various sources of starch and the starch fractions amylose and amylopectin. The δ 13 C values of amylose were consistently less negative, 0.4–2.3 ‰, than those of amylopectin in kernal starch from maize ( Zea mays ) and barley ( Hordeum vulgare ) and in tuber starch from potato ( Solanum tuberosum ). Kernel starch isolated from the maize mutants wx1 and ae1 , with known genetic lesions in the starch biosynthetic pathway, also showed significant differences in δ 13 C values. Collectively, these results suggest that variation in carbon isotope ratios in the amylose and amylopectin components of starch may be attributed to isotopic discrimination by the enzymes involved in starch biosynthesis.