Characterization of a methionine-rich protein from the seeds of Cereus jamacaru mill. (Cactaceae).

We describe here the isolation and characterization of a major albumin from the seeds of Cereus jamacaru (Cactaceae), to which we gave the trivial name of cactin. This protein has a molecular mass of 11.3 kDa and is formed by a light chain (3.67 kDa) and a heavy chain (7.63 kDa). This protein was isolated using a combination of gel filtration chromatography and reverse-phase HPLC. The amino acid composition of cactin was determined and found to resemble that of the 2S seed reserve protein from the Brazil nut, a protein remarkable for its high methionine content. The usefulness of cactin as a molecular marker in the taxonomy of the Cactaceae is discussed.