LOW-MOLECULAR-WEIGHT ALBUMINS FROM SUNFLOWER SEED - IDENTIFICATION OF A METHIONINE-RICH ALBUMIN

The small Mr, proteins of sunflower seed (Helianthus annuus) are soluble in 60% (by vol) methanol. These proteins, classified as albumins on the basis of their solubility in water, were isolated from a salt extract of sunflower seed by precipitating the 11S globulins with 60% (by vol) methanol and were resolved into eight distinct components by reversed-phase HPLC. Electrophoresis showed that each fraction contained a single polypeptide chain with an apparent Mr, in the range 10 000-18 000. The individual sunflower albumins are basic proteins with distinct amino acid compositions. The major albumins (4-8) contain high contents of glutamine/glutamic acid, asparagine/aspartic acid, arginine and cysteine, characteristic of the 2S class of seed storage proteins. One exception was the small glutamine/glutamic acid content of albumin 6. Two of the sunflower albumins (7 and 8) with Mr - 10 000 were methionine-rich proteins containing 16 residues per cent methionine as well as eight residues per cent cysteine. These sulphur-rich proteins constitute some 7% of the total salt extractable seed protein. A method for the preparation of these two albumins using a reversed-phase Sep-pak cartridge is described. © 1990.