The significance of tryptophan in human nutrition

Summary Aside from its role as one of the limiting essential amino acids in protein metabolism, tryptophan (TRP) serves as precursor for the synthesis of the neurotransmitters serotonin and tryptamine as well as for the synthesis of the antipellagra vitamin nicotinic acid and the epiphyseal hormone melatonin.By involvement in so manifold pathways, TRP and its metabolites regulate neurobehavioral effects such as appetite, sleeping-waking-rhythm and pain perception. TRP is the only amino acid which binds to serum albumin to a high degree. Its transport through cell membranes is competetrvely inhibited by large neutral amino acids (NAA). The TRP/NAA ratio in plasma is essential for the TRP availability and thus for the serotonin synthesis in the brain.Due to its high TRP-concentration, human milk protein provides optimal conditions for the availability of the neurotransmitter serotonin. Low protein cow's milk-based infant formulas supplemented with-lactalbumin — a whey protein fraction containing 5.8% TRP — present themselves as a new generation of formulas, with an amino acid pattern different from the currently used protein mixtures of adapted formulas, resembling that of human milk to a much higher degree.     

Identification of new products of S-aminoethylcysteine ketimine autoxidation

Summary In continuation of a previous work (Pecci et al., 1993), dedicated to the detection of the autoxidation products of S-aminoethylcysteine ketimine (AECK), we give here data for the identification of 2,3,6,7-tetrahydro-4H-[1,4]thiazino[2,3-b]thiazine, thiomorpholine-3-one and 5,5, 6,6-tetrahydro-2,2-dihydroxy-3,3-bi-2H-thiazine among the products of AECK autoxidation. Identification has been done on the basis of mass spectrometry and NMR spectral analyses of the isolated products.Abbreviations TLC thin layer chromatography - HPLC High performance liquid chromatography - AECK S-aminoethylcysteine ketimine     

N-Acetyl-aspartylglutamate (NAAG) in human cerebrospinal fluid: Determination by high performance liquid chromatography,and influence of biological variables

Summary NAAG is one of the neuropeptides found in highest concentrations in the CNS. The presence of micromolar concentrations of NAAG in human CSF was demonstrated by using two different and complementary analytical approaches: 1) isocratic separation of endogenous NAAG by reverse-phase high performance liquid chromatography (HPLC) with dual wavelength detection and 2) derivatization of endogenous NAAG with acidic methanol and subsequent HPLC analysis of the derivative NAAG-trimethyl ester. The NAAG concentration was between 0.44µmol/l and 7.16µmol/l (mean of 2.19 ± 1.53µmol/l) in CSF samples from forty neuropsychiatric patients. Endogenous NAAG or [³H]NAAG added to CSF samples were not significantly degraded when the CSF was incubated at 37°C during one hour, suggesting that the peptide is a highly stable metabolite in the subarachnoid space. In addition, evidence is provided that NAAG does not present a concentration gradient along the lower subarachnoid space.     

Intramitochondrial localization of alanine aminotransferase in rat-liver mitochondria: comparison with glutaminase and aspartate aminotransferase

Summary The removal of the outer mitochondrial membrane and hence of constituents of the intermembrane space in rat-liver mitochondria using digitonin showed that phosphate-dependent glutaminase, alanine and aspartate aminotransferase were localized in the mitoplasts. Further fractionation of mitoplasts following their sonication resulted in 90% of glutaminase, 98% of alanine aminotransferase and 48% of aspartate aminotransferase being recovered in the soluble fraction while the remainder of each enzyme was recovered in the sonicated vesicles fraction. These results indicated that glutaminase and alanine aminotransferase were soluble matrix enzymes, the little of each enzyme recovered in the sonicated vesicles fraction being probably due to entrapment in the vesicles. Aspartate aminotransferase had dual localization, in the inner membrane and matrix with the high specific activity in sonicated vesicles confirming its association with the membrane. Activation experiments suggested that the membrane-bound enzyme was localized on the inner side of the inner mitochondrial membrane.     

Increase in tissue cysteine level and excretion of sulfate and taurine after intragastric administration ofl-2-oxothiazolidine-4-carboxylate in rats

Summary Five mmol ofl-2-oxothiazolidine-4-carboxylate (OTC)/kg of body weight was administered into the stomach of rats, and cysteine levels in tissues and sulfate and taurine excreted in the urine were determined. The cysteine (plus cystine expressed as cysteine) concentration in the liver increased to 170–200% of the original level at 30 min and that in the blood to 160% at 60 min after the OTC administration. These high levels were maintained until 8 h after the administration and decreased gradually thereafter. Excretion of sulfate and taurine increased after the OTC administration and the increase corresponded to 26% and 15%, respectively, of the OTC administered. These findings suggest that at least about 40% of the OTC administered into the stomach was taken up and converted to cysteine, which was metabolized to sulfate and taurine.     

Structure-lipophilicity relationships of peptides and peptidomimetics

Summary Understanding the physicochemical and structural properties of peptides are important prerequisites for the rational design of bioactive peptides and peptidomimetics. The present contribution reviews methods used for the assessment and prediction of lipophilicity (or hydrophobicity) and their correlation with structural elements of peptides and closely related peptidomimetics.     

Conformational studies of chemotactic HCO-Met-Leu-Phe-OMe analogues

Summary In order to investigate the proper peptide backbone conformation able to elicit a biological activity, HCO-Met-Pro-Phe-OMe, HCO-Met-[COO]Leu-Phe-OMe, and HCO-Met-OLeu-Phe-OMe, analogues of the prototypical chemotactic peptide HCO-Met-Leu-Phe-OMe, were studied by CD and IR techniques. The results obtained comparing biological and conformational data evidence the critical presence of (i) the NH group at position 2, (ii) a rather flexible backbone, (iii) the chemical structure of the central residue which can affect the stability of a possible active conformer.     

Peptide modification by introduction ofα-trifluoromethyl substituted amino acids

Summary Methodology for the synthesis and incorporation of-trifluoromethyl substituted amino acids into N- and C-terminal position of peptides is described. The incorporation of-trifluoromethyl substituted amino acids into strategical positions of peptides enhances proteolytic stability and lipophilicity. Furthermore, it improves transport rates in vivo and permeability through certain body barriers.     

中国鳐类脑颅的研究

作者解剖观察了33种,隶于4目、7亚目、15科、19属的中国鳐类脑颅的形态。研究结果认为:锯鳐目和鳐目是原始类群,它们均具吻软骨,其中圆犂头鳐科和团扇鳐科是特化类群。电鳐目亦具吻软骨,它们是特化和退化类群。在较高等的鲼目则无吻软骨。依据鳐类不同的分类阶元,其脑颅亦各具有不同的式型。     

Complete amino acid sequence of human seminal plasma beta-inhibin. Prediction of post Gln-Arg cleavage as a maturation site

The complete sequence of a 94 amino acid human seminal plasma polypeptide exhibiting inhibin-like activity is presented. This molecule, called beta-inhibin, selectively and specifically suppresses the release of pituitary FSH in vivo as well as in vitro. It does not affect the secretion of LH. Such a novel acidic protein contains a very basic C-terminal segment which is easily cleaved by mild tryptic digestion. It is predicted that the FSH inhibiting activity may reside within this region of the molecule. This would imply a post Gln-Arg cleavage to release the basic C-terminal active moiety.