INVESTIGATIONS ON THE GUANIDINATION OF LYSINE IN PROTEINS

The present study was conducted to compare the efficacy of five differ ent reaction conditions on the guanidination of lysine in casein and t o establish optimum lysine: O-methylisourea (OMIU) for maximum guanidi nation of lysine in casein and soya bean meal. The results indicate th at the presence of glycine-NaOH buffer is not required for guanidinati on of proteins at pH 10.5. A OMIU concentration of 0.4 M was found to be as effective as 0.6 M for guanidination. Both OMIU-hydrogen sulphat e and free OMIU were equally effective reagents in terms of conversion of lysine to homoarginine. The use of OMIU-hydrogen sulphate for guan idination and the use of ethanol to recover guanidinated protein, howe ver, resulted in the formation of crystalline sodium sulphate, a known purgative agent, in the guanidinated material, and therefore are not recommended if the guanidinated protein is to be used in animal trials . The molar ratio of lysine:OMIU required for efficient lysine convers ion to homoarginine varied for different protein sources. Ratios requi red for maximum conversion for casein and soya bean meal were determin ed to be 1:10 and 1:16, respectively. A simple procedure developed for the large-scale guanidination (5-10 kg batches) of proteins is also d escribed. The results showed that guanidination of proteins can be eas ily scaled up from 20 g to 5-10 kg and that large-scale guanidination is feasible and efficient.