Carbon isotope ratios of amylose,amylopectin and mutant starches

Carbon isotope ratios (expressed as δ¹³C values) were determined for various sources of starch and the starch fractions amylose and amylopectin. The δ¹³C 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 δ¹³C 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.