Investigations on the Guanidination of Lysine in Proteins

Abstract

The present study was conducted to compare the efficacy of five different reaction conditions on the guanidination of lysine in casein and to establish optimum lysine:O‐methylisourea (OMIU) for maximum guanidination of lysine in casein and soya bean meal. The results indicate that the presence of glycine–NaOH buffer is not required for guanidination 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 sulphate and free OMIU were equally effective reagents in terms of conversion of lysine to homoarginine. The use of OMIU–hydrogen sulphate for guanidination and the use of ethanol to recover guanidinated protein, however, 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 conversion to homoarginine varied for different protein sources. Ratios required for maximum conversion for casein and soya bean meal were determined 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 described. The results showed that guanidination of proteins can be easily scaled up from 20 g to 5–10 kg and that large‐scale guanidination is feasible and efficient.

Effects of carbadox or formic acid and diet type on ileal digestion of amino acids by pigs

“…To determine the TID and endogenous flow of lysine, the pigs were fed diets in which 50% of soyabean meal was replaced with guanidinated soyabean meal prepared in a 0.6 M O-methylisourea solution at pH 10.5 for 6 d (Imbeah et al, 1996). Prior to the homoarginine feeding, the pigs were fed three protein-free meals.…”

Use of the guanidination reaction for determining reactive lysine, bioavailable lysine and gut endogenous lysine

“…Maga (1981) also noted that the pH of the incubation mixture would drop during incubation at a rate of 0.1-0.2 pH units per 24 h and recommended pH adjustment on a daily basis. OMIU can be used as the buffer for maintaining the pH of the guanidination reaction mixture (Imbeah et al 1996). However, the low OMIU to lysine ratio used by Maga (1981) meant that as OMIU was consumed by the guanidination reaction, the amount of unreacted OMIU (the buffer) decreased and the pH dropped.…”

“…For guanidinating the proteins in foods and feedstuffs, OMIU has been used as either the free base (Eklund et al 2013;Friesen et al 2006;Imbeah et al 1996;Mao et al 1993;Pahm et al 2010;Ravindran et al 2004;Rutherfurd and Moughan 1990;Torbatinejad et al 2005) or as the hydrogen sulphate salt (Fontaine et al 2007;Imbeah et al 1996). While the use of the free base is more prevalent, both forms of OMIU have been reported to be equally effective at guanidinating proteins (Imbeah et al 1996).…”

“…While the use of the free base is more prevalent, both forms of OMIU have been reported to be equally effective at guanidinating proteins (Imbeah et al 1996). The free base form of OMIU is commonly prepared from the hydrogen sulphate form after removal of the sulphate by precipitation with barium hydroxide.…”

Protein quality of pig diets : processing effects on amino acid digestibility and post-absorptive utilization

“…Conversion of Lys to homoarginine in the latter study, however, was calculated as the molar amount of homoarginine divided by the sum of the molar amounts of homoarginine and unreacted Lys. This manner of expressing conversions is often used (Maga, 1981;Rutherfurd and Moughan, 1990;Imbeah et al, 1996;Ravindran et al, 1996;Zhang et al, 2006;Pahm et al, 2008) but does not take into account the conversion of Lys to double derivatized Lys or other Lys derivatives. When applying this equation to the data of the current study, conversions of > 90% were found (data not shown).…”