To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.

This paper reports the occurrence of protein-protein co-precipitation, through electrostatic interactions. As a preliminary overview the effect of mixing lysozyme with a range of proteins (BSA, P-lactoglobulin, sodium caseinate and whey isolate) was tested by turbidity measurements. Turbidity increased when the proteins were mixed with lysozyme in water and not in phosphate buffer. The exception was the interaction of whey isolate and sodium caseinate which showed turbidity (but not precipitation) when mixed with lysozyme in phosphate buffer. Further detailed studies on the interaction between whey proteins a-lactalbumin and P-lactoglobulin and hen egg lysozyme by fast protein liquid chromatography (FPLC), have shown that, in aqueous solution of pH 6.8, a higher level of interaction occurred between lysozyme and P-lactoglobulin compared with lysozyme and a-lactalbumin. A similar interaction was not observed between a-lactalbumin and 0-lactoglobulin. The predominant product of the interaction was an insoluble precipitate. In addition, a small amount of soluble complex was also recovered by ion-exchange chromatography of the supernatant. The soluble complex was shown by SDS-polyacrylamide gel electrophoresis to comprise the same components as the insoluble precipitate, i.e. lysozyme and a-lactalbumin or lysozyme and P-lactoglobulin. The interactions of the proteins and the amount of precipitation varied depending on the concentration of each protein in the mixture, the ionic strength and pH of the solution. Molecular modelling studies, using interactive docking of the crystal structures, indicated that for the P-lactoglobulin-lysozyme interaction the optimum visual fit could involve electrostatic interactions between Glutamate 35 and Aspartate 53 in the catalytic binding site on lysozyme and Lysines 138 and 141 at the dimerization site of P-lactoglobulin. For a-lactalbuminlysozyme mixtures, however, the modelling suggested that non-specific electrostatic binding may occur.

No abstract

No abstract