The patterns of Cd-binding proteins in rice and wheat seed and their stability

The protein-binding forms of cadmium in polluted rice and wheat seeds and their stability were investigated using the methods of Sephadex chromatography. Three absorption peaks (F-I, F-II and F-III) were identified in Tris-HCl extraction of rice and wheat on Sephadex G 75. The Cd in the protein extracts from rice and wheat seeds was distributed mainly in the fractions of F-I and F-III. The apparent molecular weights of Cd-binding proteins for F-I and F-III were 54.5 and 5.5 KD, respectively. The components of amino acid for the protein bound with heavy metals were different. There were high contents of glutamic acid, cysteine, valine, isoleucine, leucine and tyrosine in the protein extracts of rice and wheat. After cooking, the Cd-binding proteins were destroyed. High molecular weight protein-binding form (54.5 KD) was broken into low molecular weight complex (5.5 KD) or tiny peptide chain. Simultaneously, Cd bound with protein was released, or mainly bound with protein of smaller molecular size. Enzyme treatment (pepsin and trypsin) also caused a destruction of Cd binding protein and a change in the distribution of Cd in the eluent. The concentrations of Cd in the elution of first and third peak decreased markedly, and the Cd distribution was observed in the elution after third peak (F-III).