Uptake of acetylated peptides from the small intestine in sheep and their nutritive value in rats

Abstract

Acetylation is a potential method for protecting dietary peptides from degradation by rumen micro-organisms. As a first step in determining the nutritive value of acetylated peptides, their disappearance in the small intestine of sheep and their ability to support growth in a rat bioassay were measured. 15 N-labelled peptides were prepared from lucerne which had been grown with 15 N-labelled (NH 4 ) 2 SO 4 in the absence of Rhizobium. Peptides were prepared by enzymic hydrolysis of the extracted protein. Two peptide preparations were made using different proteinase mixtures. These mixtures contained peptides with an average molecular weight of 559 and 522 Da. They were treated with acetic anhydride, which resulted in 85 and 88 % modification respectively, and their uptake from the small intestine was determined by injecting 1 g of untreated or acetylated peptides in a Cr-EDTA solution into the jejunum of two sheep fitted with jejunal catheters and ileal cannulas. Ileal digesta were collected and analysed for Cr and 15 N. The uptake of dialanine (Ala 2 ) and N-acetyl-Ala 2 were compared in a similar way. The disappearance of 15 N from lucerne peptides was high (88 and 93 % respectively) and this was not affected significantly by acetylation (86 and 87 %). Corresponding values for Ala 2 and N-acetylAla 2 were both 96 %, as measured by HPLC. It was therefore concluded that acetylation did not affect the uptake of peptides from the small intestine in sheep. Two feeding trials were carried out with rats. The first trial was carried out with a protein-free diet to which was added 10 % lactalbumin or 5 % lactalbumin and then a mixture of methionine-free amino acids, either alone or supplemented with Met, Gly-Met or acetylated Gly-Met. The rats grew equally well on all sources of Met, but failed to grow significantly on the mixture of Met-free amino acids. In the second trial the diet contained casein as 5⋅9 % of the basal diet. Additional casein, pancreatic casein hydrolysate (peptides) and acetylated pancreatic casein hydrolysate (acetylated peptides) were compared as sources of amino acids, at inclusion rates of 100 g/kg final diet. Feed intake was similar with casein and peptides treatments, but was depressed by 23 % with acetylated peptides. Live weight gain was 15 and 75 % lower with the peptides and acetylated peptides diets respectively. Addition of lysine, arginine or histidine did not restore feed intake or weight gain of rats receiving acetylated peptides, but feed intake was restored immediately when peptides replaced acetylated peptides. When intake was restricted to 9 g/d and acetylated casein hydrolysate replaced half of the protein in the diet, rats gained weight less rapidly (1⋅44 v: 1⋅09 g/d) and retained less N, such that only 0⋅36 of the acetylated peptide-N was calculated to remain available to the animal. This N retention compared with 0⋅70 for unmodified casein. Thus, the rat bioassay indicated that certain specific peptides may well be of high nutritive value following acetylation, but that there...

Effect of acetylated soyabean peptides on rumen fermentation and nitrogen metabolism in sheep

“…The result was similar with that of Wallace et al (1998), who injected acetylated peptides into the duodenum of sheep. It is clear that these in vivo studies suggest a benefi t from acetylation in controlling ruminal breakdown and providing nitrogen to ruminants.…”

Specific enhancement of acylase I and acylpeptide hydrolase activities by the corresponding N‐acetylated substrates in primary rat hepatocyte cultures

“…As N-Ac-L-Met and N-Ac-L-Val exerted activating effects on the ACY I activity, the APH (treated cells/untreated cells) /ACY I (treated cells/untreated cells) ratio dropped from 1.0 to 0.26-0.34, whereas in the presence of N-Ac-L-Met-L-Ala and N-Ac-L-Ala-L-Ala this ratio increased to 3.7-4.5, so that each type of substrate had specific effects on the corresponding enzyme. The results of the present study therefore show that both aminoacids and N-acetylated peptides are apparently able to cross the hepatocyte plasma membrane as efficiently as their unmodified counterparts, in agreement with previous uptake studies on rabbit (Brachet et al, 1991) and sheep (Wallace et al, 1998) small intestine. There are no procedures available so far to our knowledge for specifically studying the uptake of N-acetylated peptides without any interference from the products of hydrolysis by the liver cells.…”

“…Deletions of the locus are known to occur in various types of carcinomas including the small cell lung carcinoma and that of renal cells (Naylor et al, 1989;Miller et al, 1989;Erlandsson et al, 1991). Although the uptake of N-acetylated aminoacids and peptides from small intestine has not yet been fully documented (Brachet et al, 1991;Wallace et al, 1998), N-Ac-L-Met has been found to be readily available for protein synthesis in the growing rat (Rostruck and Boggs, 1975;Puigserver et al, 1978).…”

Toxicological evaluation of acetylated faba bean globulin

“…The same results were found with acetylated pancreatic casein hydrolysate. Under circumstances of restricted feeding in order to eliminate the intake effect, the acetylated hydrolysate retained about half of the nutritive value of unmodified casein hydrolysate 22…”

“…It is known that acetylated peptides are absorbed from the small intestine. Moreover, intestinal aminopeptidase N , N ‐acylpeptide hydrolase and acylase I have been found to be responsible for the biological utilisation of N‐acetylated food proteins 19–22. However, until now a detailed assessment of the safety of acetylated faba bean globulin has not been performed.…”