Non-protein Tryptophan Research Articles

The content of protein and non-protein (free and protein-bound) tryptophan in Theobroma cacao beans

The contents of protein and non-protein (free and protein-bound) tryptophan and of proteins in cocoa beans of various origin were determined. Protein concentrations varied from 11.8 g/100 g in beans from the Dominican Republic to 15.7 g/100 g in roasted beans from the Ivory Coast. The highest protein tryptophan content was found in cocoa beans from Ecuador. Madagascar beans had the highest value of free tryptophan and Echeandia the lowest (17.26 and 6.39 mg/100 g, respectively). Tryptophan was bound to water-soluble proteins as well as to proteins soluble in buffer solution (pH 8.9) and in 70% ethanol. In particular, Dominican Republic cocoa contained the highest amount of tryptophan bound to water-soluble proteins. Very little tryptophan was linked to proteins soluble in alkaline or ethanol solutions, and values ranged from 0.96 to 3.04 and from 0.24 to 1.21 mg/100 g of dry defatted cocoa sample, respectively.

Non-protein (free and protein-bound) tryptophan content in cereal and legume seed flours

Abstract Cereals and legumes are the major source of protein in the human diet. There is little information on the presence of non-protein tryptophan, one of the essential amino acids less represented in the vegetable proteins. Our results show that tryptophan is present not only in the free-form but also is linked either to water soluble proteins or to proteins extracted at pH 8.9 both in cereal and legume flours. As regards the cereals, wheat and spelt contain the highest content of protein tryptophan and maize the lowest. Spelt, followed by barley and pearl millet flours, contains the highest amounts of free tryptophan and the rice the lowest. In addition, spelt flour shows the highest levels of tryptophan linked to both water soluble and buffered protein fractions, whereas rice contains the lowest amounts of protein-bound tryptophan. Among the legume flours, soybeans show the highest value in protein tryptophan and peas the lowest. Chick peas contain the highest concentrations of both free and protein-bound tryptophan water soluble fraction. This last fraction appears absent in broad bean, lentil and soybean flours. In addition, beans are shown to contain the highest levels of tryptophan linked to proteins extracted at pH 8.9, and peanuts the lowest values both as free and protein-bound forms. Considering that tryptophan is one of the limiting amino acids of the biological value of vegetable proteins, the determination of non-protein tryptophan in food is very useful in calculating the score.

Protein and non-protein (free and protein-bound) tryptophan in legume seeds

The contents of protein and non-protein (free and protein-bound) tryptophan and of proteins in the flours of nine legume seeds were determined. Lupins and soybeans showed the highest protein concentrations, followed by groundnuts, beans, broad beans, lentils, vetches, chick-peas, and peas. Protein tryptophan content is higher in soybeans and lower in peas (502 and 192 mg/100 g of dry flour, respectively) than in the other legumes, which also contain non-protein tryptophan. Chick-peas show the highest value of free tryptophan and groundnuts the lowest (58.2 and 2.24 mg/100 g of dry flour, respectively). Tryptophan appears to be bound to water-soluble proteins and to proteins soluble at pH 8.9. In particular, chick-peas contain a high amount of tryptophan bound to water-soluble proteins, followed by beans. The results are evaluated, considering the importance, not only of protein, but also non-protein tryptophan, for assessing the nutritive value of a protein in foods.

The content of proteic and nonproteic (free and protein-bound) tryptophan in quinoa and cereal flours

The content of proteic and nonproteic (free and protein-bound) tryptophan and of proteins in quinoa, wheat, rice, maize, barley, oat, rye, spelt, sorghum and millet flours was determined. Protein content and proteic tryptophan of quinoa were similar to that of wheat and spelt, but higher than in other cereals. Free tryptophan in quinoa flour showed values similar to those of wheat, oat and sorghum Kalblank, lower than those of barley, spelt and pearl millet, but higher than in rice, maize, rye, sorghum DK 34 – Alabama hybrid. In addition, nonproteic tryptophan appears bound both to water soluble proteins and to proteins soluble at pH 8.9. The results are discussed regarding the importance of the nonprotein tryptophan fraction, the only one able to enter the brain, that is more easily absorbed, so guarantees a greater amount available for uptake by the central nervous system.

Non-protein tryptophan in foods.

Our previous papers (Allegri et al, 1993; Biasiolo et al., 1995) have shown that milk and yoghurt contain non-protein tryptophan. It was known that these foods contain free amino acids, although free tryptophan was not determined for methodological reasons (George and Lebenthal, 1981; Miller and Kandler, 1964; 1966; 1967a; 1967b).

Determination of nonprotein tryptophan in yoghurts by selective fluorescence and HPLC

The concentrations of total nonprotein (protein-bound and free) and free tryptophan were determined in various kinds of market yoghurts prepared from raw, skimmed or partially skimmed cow's milk, with or without fruit, coffee or cereals. The mean values of total nonprotein tryptophan in plain yoghurt made from whole or skimmed milk were 3.45 ± 0.46 and 3.25 ± 0.38 mg/kg, respectively, that is, five to six times higher than in cow's milk. Instead, the free fraction of tryptophan was 2.76 ± 0.50 and 2.44 ± 0.36 mg/kg, respectively (seven to eight times higher than in cow's milk). In yoghurts with fruit, the mean values were quite similar to those of plain yoghurt, although they varied within each type of yoghurt. The highest contents of both fractions of nonprotein tryptophan were found in yoghurts with coffee or cereal, due to the contribution of these kinds of food. The increase in free tryptophan in yoghurt improves its nutrition value, as more tryptophan is made available for the brain synthesis of the neurotransmitter serotonin, of which tryptophan is the precursor.

Content of non-protein tryptophan in human milk, bovine milk and milk- and soy-based formulas

Variations in the content of total non-protein (protein-bound + free) and free tryptophan in human and bovine milk after delivery, soy ‘milk’, and adapted formulas based on bovine milk and soybean protein are reported. Colostrum contains much more of both forms of non-protein tryptophan than mature human milk and bovine milk, and the percentage of free tryptophan is also higher in human milk. Fresh commercially available bovine milk contains amounts of non-protein tryptophan similar to those of bovine milk 1 month after delivery. However, these levels are much lower than those observed in soy ‘milk’. Both forms of non-protein tryptophan are also much higher in soybean than in bovine milk formulas, although there are some differences among the kinds of formulas. However, values are significantly lower than in colostrum. The differences in the content of non-protein tryptophan are discussed.

Mechanism of decline in rat brain 5-hydroxytryptamine after induction of liver tryptophan pyrrolase by hydrocortisone: roles of tryptophan catabolism and kynurenine synthesis.

1 Two mechanisms have been proposed to explain the decline in brain tryptophan and 5-hydroxytryptamine (5-HT) after administration of hydrocortisone and the subsequent induction of liver pyrrolase. These are depletion of tryptophan by high rates of tryptophan catabolism and inhibition of tryptophan uptake by elevated levels of the tryptophan catabolite, kynurenine.2 The increase in plasma kynurenine after hydrocortisone injection (25 mg/kg) was small, and kynurenine, at a concentration ten fold greater, did not inhibit tryptophan uptake by brain as measured by the Oldendorf technique. Thus, inhibition of tryptophan uptake by kynurenine is not an important mechanism in the control of brain tryptophan and 5-HT.3 The decline in brain tryptophan after hydrocortisone was comparable to that seen in other tissues, which comprise more than half of the body weight of a rat.4 The total decline in free tryptophan stores in whole animals treated with hydrocortisone was estimated to be about 450 mug. This amount of tryptophan would be catabolized by tryptophan pyrrolase in about 20 min, when the enzyme is induced, according to an earlier estimate of the rate of tryptophan catabolism in vivo.5 Tryptophan pyrrolase activity remains high for much longer than 20 min, suggesting that there is net protein catabolism, which releases tryptophan and prevents non-protein tryptophan levels falling very far.6 These results demonstrate that the decline in brain tryptophan and 5-HT after hydrocortisone is caused by depletion of tryptophan stores due to the high activity of tryptophan pyrrolase. However, our data suggest that this effect is diminished by release of tryptophan from proteins. Thus, peripheral protein metabolism may be an important factor in the control of brain tryptophan levels and 5-HT synthesis.

A PHYSIOLOGICAL STUDY OF THE VERMILION EYE COLOR MUTANTS OF DROSOPHILA MELANOGASTER

HE vermilion eye color mutant Drosophila melanogaster was one of the Tmutants used by BEADLE, EPHRUSSI, TATUM and their collaborators in their early attempts to interpret the biochemical effects of genes (Cf. Review by EPHRUSI 1942). More recent studies on vermilion mutants (GREEN 1949, 1952, 1954) made it seem worthwhile to pursue further the study of the physiological effects of these mutants. The sex-linked, recessive vermilion ( U ) eye color mutants of D. melanogaster are characterized phenotypically by a lack of brown eye pigment under the usual genetic and environmental conditions. GREEN ( 1952) distinguished two series of vermilion mutants by their differential interaction with a nonallelic X chromosome mutant, suppressor of vermilion (su-U) . One group of u mutants approaches wild type in the production of brown eye pigment when combined with SU-U. This series may be designated us, indicating that it is suppressible by su-U. The other series may be designated vu, since it is unsuppressed by su-U. GREEN (1954) reported crossing over between a us allele ( U ’ ) and a vu allele ( ~ ~ ~ f ) indicating that they are pseudoallelic to each other. BARISH and Fox (1956) report that the vu mutant, uAsa, is allelic to v’ and pseudoallelic to STURTEVANT (1920) demonstrated by the use of gynandromorphs that the ~ ( u ’ = u s ) mutant was nonautonomous in development; i.e., flies which have genetically u eye tissue, but also contain U + tissue, may have phenotypically U + eyes. Transplantation of optic discs from u larvae into wild type larvae (EPHRUSSI and BEADLE 1935) confirmed the nonautonomous development of u with respect to wild type tissue. GREEN (1952) established developmental nonautonomy of the vu mutants ( ~ ~ ~ f , usla, u5lc) with respect to wild type tissue in gynandromorphs. Studies by TATUM (1939), TATUM and HAAGEN-SMIT (1941 ) , BUTENANDT, WEIDEL and BECKER (1940) and KIKKAWA (1941 ) establishcl i h genetically u flies will produce brown eye pigment if supplied with the tryptuphan metabolite, kynurenine, either by injection or in the larval food. GREEN (1949) found that large quantities of nonprotein tryptophan are dccumulated by flies carrying U’. Either kynurenine or its precursor, formylkynurenine, was shown to act as a precursor for brown eye pigment for both U’ ( u s )