ISOLATION CHARACTERIZATION OF THE MAJOR ALBUMIN FROM COLOCASIA-ESCULENTA CORMS

The major albumin from Colocasia esculenta corms was isolated using differential solubility and gel-filtration chromatography. It corresponds to 11% of the total soluble protein that accumulates in the corms. The native protein has an Mr of 50 000 and appears to be composed of homogenous subunits with Mr of approximately 8300 in denaturing gels. Isoelectric focussing and two-dimensional electrophoresis demonstrate the presence of three isoforms. The major one, accounting for more than 90% of the protein, has an pI of 6.1. The two minor ones have pI values of 5.3 and 5.7. The isolated protein has a relatively high content of essential amino acids such as phenylalamine and leucine but is poor in sulphur-containing amino acids. Western blotting analysis has shown that the expression of the protein is enhanced in the corm and that the residual expression observed in lamina and petiole corresponds to a larger protein, although lamina expresses both species. No expression has been observed in roots. The protein also seems to accumulate in Caladium spp. corms, where it appears to be larger, but not in the storage Xanthosoma sagitifolium, Xanthosoma atrovirens, Ipomoea batatas, Daucus carota, Solanum tuberosum and Manihot esculenta. © 1990.