Metabolism of heat-damaged proteins in the rat. Inhibition of amino acid uptake by "unavailable peptides" isolated from enzymic digests of heat-damaged cod fillet

1. An extract containing "unavailable" small peptides was isolated from an enzymic digest of heat-damaged cod fillet and examined for its influence on uptake of leucine in the rat small intestine, using the everted-sac technique. 2. The extract strongly inhibited the uptake of leucine. It had no effect on uptake of glucose or its metabolism to lactate. 3. The findings are discussed in relation to the concept (Buraczewski, Buraczewska & Ford, 1967) that the accumulation of "unavailable peptide" material in the intestine, found in rats given heat-damaged protein, might hinder the absorption of amino acids by blocking a mechanism involved in their transport across the mucosal barrier.

Square pegs in round holes: a study of residents in long-term institutions in London, Ont

A large random sample of people in the long-term institutions (homes for the aged, nursing homes and continuing care hospitals) of London, Ont. was studied to assess the suitability of these people, according to physical and mental status, for the institution in which each resided. The results indicated a relative need for beds in homes for the aged and nursing homes. A high proportion (29% to 54%) of people in the three types of institutions were unsuitably placed. Greater flexibility is needed in institutional arrangements, and institutions should be examined for their potential to provide support in maintaining the elderly at home. The findings of this study add some weight to the arguments of those calling for more and better home care programs for the disabled.

An improved procedure for the assay of available lysine and methionine in feedstuffs using Tetrahymena pyriformis W

1. A study was made of the assay of available lysine and available methionine using Tetrahymena pyriformis W, as applied to a variety of protein-rich feedstuffs. 2. Results were strongly influenced by the conditions under which the analyses were done. With most of the test samples predigestion with papain caused a large increase in the values obtained. 3. An improved assay procedure was developed which included enzymic predigestion of the test samples, "all-in" sterilization of the medium constituents, and measurement of growth from extinction values. It gave results for available lysine that were broadly similar to those obtained in growth tests with rats, and in chemical tests by the method of Carpenter (1960). Values for available methionine agreed closely with those obtained in microbiological tests with Streptococcus zymogenes.

Metabolism of heat-damaged proteins in the rat. influence of heat damage on the excretion of amino acids and peptides in the urine

1. Freeze-dried cod muscle and casein were subjected to various conditions of heat treat-ment. Diets containing the different products, or the unheated materials, were given to a group of four adult male rats during successive 48 h periods, and urine was collected during the second 24 h of each 48 h period. A further collection of urine was made from the rats after they had been given protein isolated from heated skim-milk powder. The content and amino acid composition of the ‘peptide’ and ‘free amino acids’ in the urines were determined.

2. Heat damage to the cod-fillet protein increased the total urinary excretion of peptide-bound amino acids, from 18·6 to 48·8 µmol/rat.d. The composition of the peptide also changed, and in particular there was a marked increase in lysine, from 2·98 to 20·30 µmol %. Three amino acids - lysine, aspartic acid and glutamic acid - together comprised nearly 70 % of the total amino acid residues. There was a corresponding increase in urinary excretion of free amino acids, from 53·7 to I 14·4 µmol/rat.d. The combined losses of lysine in urinary peptide and free amino acids were 1·5 % of the total lysine ingested, as against 0·3 % for the unheated cod fillet.

3. The effects of similar heat treatment of casein on the composition of the urinary peptide and free amino acids were less marked. There was no increase in total urinary peptide excretion and there was a smaller increase in the lysine content of the peptide.

4. In urine of rats given protein isolated from heated skim-milk powder, the peptide hydro-lysate was rich in lysine and in furosine, which together comprised 41 mol % of the total amino acid composition. These compounds were presumably formed, together with a smaller quantity of pyridosine, from lysine-carbohydrate complex in the urine. It is probable that, as compared with free lysine, the lysine-carbohydrate complex was absorbed relatively in-efficiently from the rat intestine.

5. The findings are discussed in relation to the wider question of the metabolism of the ‚unavailable peptide’ that is released in the course of digestion of heat-damaged protein.