Protein-bound D-amino acids, and to a lesser extent lysinoalanine, decrease true ileal protein digestibility in minipigs as determined with (15)N-labeling. (1/5)

Heat and alkali treatment of food may increase the concentrations of protein-bound D-amino acids and cross-links such as lysinoalanine (LAL). To examine how protein treatment affects digestibility, purified test meals [total protein 150 g/kg dry matter (DM), 0.44 MJ/(kg BW(0.75). d)] were prepared, containing (g/kg DM) casein, 75; beta-lactoglobulin, 50; or wheat protein, 40. Each was (15)N-labeled. Test proteins were used either in their native form or after treatment for 6 or 24 h at 65 degrees C, pH 10.5-11.5. Each meal was fed to nine adult miniature pigs (twofold complete cross-classification). Chyme was collected continuously over 33 h postprandially via T-fistulas in the terminal ileum, and digestibilities of test proteins and individual L- and D-amino acids were calculated on the basis of recovery of (15)N and the respective amino acids in the chyme. Treatment of casein, beta-lactoglobulin or wheat protein for 24 h increased levels of D-amino acid residues. L-Asparagine and aspartate (L-Asx) were particularly susceptible; 14. 7 +/- 0.4, 11.7 +/- 0.2 and 11.0 +/- 0.9%, respectively, underwent racemization. LAL levels increased in parallel; 11.7 +/- 0.3, 13.6 +/- 0 and 14.8 +/- 0.0%, respectively, of total lysine was converted to LAL. At the same time, prececal protein digestibility was decreased by 13.4 +/- 2.3, 15.3 +/- 1.4 and 17.8 +/- 1.2% units, respectively (P < 0.05; mean +/- SEM, n = 9). Digestibility of individual L-amino acids decreased by 10-15%, but L-amino acids prone to peptic cleavage, such as L-phenylalanine and L-tyrosine, were not affected. Digestibilities of D-amino acids and LAL were approximately 35%. It seems that mainly D-amino acids, and to a lesser extent LAL, were responsible for lower digestibility by interfering with peptic cleavage.  (+info)

Nine post-translational modifications during the biosynthesis of cinnamycin. (2/5)

 (+info)

Studies on the utilization of lysinoalanine and lanthionine. (3/5)

Studies were conducted to determine the nutritional value of lysinoalanine for rats and chicks and the nutritional value of lanthionine for chicks. For each experiment, purified crystalline amino acid diets and crystalline lysinoalanine and lanthionine were employed. Results indicated that the lysine moiety of lysinoalanine is completely unavailable to the rat and only partially available to the chick. Of 10 rats fed lysinoalanine, seven developed nephrocytomegaly. The lanthionine studies indicated that the cysteine moiety of lanthionine is 32% available when fed as the racemic mixture and 52% available when fed as the L-DL-isomeric mixture. Thus, it appears that lysinoalanine formation in alkali-treated proteins results in a corresponding decrease in nutritionally available lysine. However, the lanthionine formed under similar conditions results in loss of only one-half of the corresponding level of nutritionally available cysteine.  (+info)

Excretion and tissue distribution of radioactive lysinoalanine, N epsilon-DL-(2-amino-2-carboxyethyl)-U-14C-L-lysine (LAL) in Sprague-Dawley rats. (4/5)

Rats were fed either a control soybean protein diet or a diet containing 3,000 ppm soybean protein-bound lysinoalanine (LAL) for 4 or 6 weeks, at which time all rats were dosed by stomach tube with 14C-LAL labeled in the lysine moiety. Urinary and fecal excretion and tissue distribution were followed in one experiment at 6, 12, 18, 24, 48 and 72 hours. Excretion in urine, feces and expired air was followed in the other metabolic experiment at 2-hour intervals for 48 hours, and at 24-hour intervals for the next 7 days. Tissue samples were counted and LAL determination was made by amino acid analysis in both experiments. The group of rats fed LAL excreted slightly more LAL than the group fed the control diet. Very little LAL remained in the rat tissues after either experiment, and the largest remaining quantity of radioactivity was found as lysine. Quantitation of 14C-lysine in the original material and in the material from rat organs showed that the rat has some capacity for converting LAL to lysine. Less than 0.5% of the original 14C remained in any organ examined 9 days after dosing in the either control or LAL-fed rats. Autoradiographs of the kidneys 24 hours after dosing showed that the radioactive material had accumulated in the proximal convoluted tubules of the corticomedullary junction.  (+info)

Lysinoalanine as a metal chelator. An implication for toxicity. (5/5)

Synthetic lysinoalanine (N epsilon-DL-(2-amino-2-carboxyethyl)-L-lysine) was found to have a strong chelating ability for metals. It became colored when mixed with Cu+2 and showed absorption characteristics typical of a complex. Lysinoalanine could inactivate metalloenzymes such as carboxypeptidases A and B and yeast alcohol dehydrogenase, by removing the zinc ion from the active site. Model building for a mononuclear complex of the metal and lysinoalanine with space-filling models was possible for the LD-isomer, N epsilon-D-(2-amino-2-carboxymethyl)-L-lysine. Etiological studies of its toxicity to humans should be made because the chelating ability of lysinoalanine is sufficiently strong to remove the metal from the enzyme active center at millimolar concentration.  (+info)