Are aromatic residues essential at the "active sites" of peptide hormones?

Solvent Effect in Catalytic Lignin Hydrogenolysis

The solvent effect in the catalytic depolymerization of the three-dimensional network of lignin is discussed based on recent reports in this field. Also, the results of an experimental study on the depolymerization of kraft lignin are presented. The cleavage of ether bonds within the lignin network was promoted using ruthenium and platinum on activated carbon (Ru/C and Pt/C), two common hydrogenolysis catalysts. Methanol was identified as a suitable solvent. Noteworthy, under the chosen reaction conditions, the catalysts showed significant resilience to the sulfur present in kraft lignin. The conversion of kraft lignin to lignin oil was strongly affected by the reaction conditions. Although the Ru/C catalyst provided the highest yield at supercritical conditions, a maximum yield was obtained for the Pt/C catalyst at near-critical conditions. The formation of guaiacol, 4-alkylguaiacols, isoeugenol, and 4-ethyl-2,6-dimethoxyphenol is attributed to the solubility of oligomeric lignin fragments in the solvent and the relative propensity of specific groups to adsorb on the catalyst surface.

Pyridyl-alanine as a Hydrophilic, Aromatic Element in Peptide Structural Optimization

Glucagon (Gcg) 1 serves a seminal physiological role in buffering against hypoglycemia, but its poor biophysical properties severely complicate its medicinal use. We report a series of novel glucagon analogues of enhanced aqueous solubility and stability at neutral pH, anchored by Gcg[Aib16]. Incorporation of 3- and 4-pyridyl-alanine (3-Pal and 4-Pal) enhanced aqueous solubility of glucagon while maintaining biological properties. Relative to native hormone, analogue 9 (Gcg[3-Pal6,10,13, Aib16]) demonstrated superior biophysical character, better suitability for medicinal purposes, and comparable pharmacology against insulin-induced hypoglycemia in rats and pigs. Our data indicate that Pal is a versatile surrogate to natural aromatic amino acids and can be employed as an alternative or supplement with isoelectric adjustment to refine the biophysical character of peptide drug candidates.

Synthesis and conformational analysis of His-Phe-Arg-Trp-NH2 and analogues with antifungal properties

The synthesis, in vitro evaluation, and conformational study of His-Phe-Arg-Trp-NH2 and related derivatives acting as antifungal agents are reported. Among them, His-Phe-Arg-Trp-NH2 and His-Tyr-Arg-Trp-NH2 exhibited antifungal activity against Cryptococcus neoformans. Antifungal activity of these compounds appears to be closely related to the alpha-MSH effect. A conformational and electronic study allows us to propose a biologically relevant conformation for these tetrapeptides acting as antifungal agents. In addition, these theoretical calculations permit us to determine the minimal structural requirements to produce the antifungal response and may provide a guide for the design of compounds with this biological activity.

Biochemical problems of regulation by oligopeptides

Some problems are considered which arise in biochemical studies on structure and function of natural oligopeptides consisting of 2-50 amino acid residues. The problems under consideration include the generation of oligopeptides from precursors, chemical structure, the role of functionally important radicals and spatial configuration, and structure-function relationships. Different types of regulation are shown mainly for oligopeptides involved in muscle contraction.

Amino acid sequence pattern in the regulatory peptides

The essential properties of the primary structure of regulatory peptides, i.e. amino acid residues and their combinations, which are characteristic of the whole population of regulatory peptides, have been revealed using statistical methodology. These properties are as follows: increased content of certain residues (Gly, Pro, Phe, Arg, Tyr, Met and Trp) as well as an increased rate of occurrence of certain pairs of residue as compared with proteins, a random sequence of residues and "nonregulatory" peptides. By representing regulatory peptides as a sequence of hydrophobic (2 types) and hydrophilic (3 types) segments, the pattern for alternation of these segments in regulatory peptides has been determined. The segments were classified into 5 types according to the peculiarities of mutual localization of hydrophobic and hydrophilic residues within the primary structure of regulatory peptides. As compared with proteins, "nonregulatory" peptides and a random sequence of segments, regulatory peptides were characterized by an increased frequency of 4 particular pairs of segments among 12 theoretically possible pairs. These 4 pairs are fragments of the periodic segment sequence with periods of 4 segments. The revealed pattern indicates that there exists a general principle of the regulatory peptide primary structure organization and possibly a common type of the regulatory peptides flexible peptide chain folding at the ligand-receptor complex formation.

A few distinct 'molecular sandwiches' are basis for structural and functional similarities of subspecies of interferon alpha and of families of growth-promoting hormones

'Molecular sandwiches' composed of two aromatic amino acids separated by a hydrophilic one were found on eleven subspecies of human interferon alpha, on murine interferon alpha 2, and human interferon beta 1. In addition, another type of the sandwiches was found on several species of interferon. This confirms and extends the observations concerning the similarities between some interferons and several classical hormones. Furthermore, we are presenting evidence that a distinct type of the 'molecular sandwiches': Tyr-Cys...Cys and/or Cys...Cys-Cys...Cys, that participate in formation of disulfide bonds, is a characteristic marker of most, if not all of the growth-promoting hormones including growth factors. The 'sandwiches' appear to be important for receptor binding.

Synthesis and biological activity of [L-3,4-dehydroproline3]-tuftsin

A 3,4-dehydroproline analogue of tuftsin (L-Thr-L-Lys-L-Pro-L-Arg) was prepared by the solid phase synthetic method. Following reversed-phase high performance liquid chromatography (HPLC) purification, the analogue was compared to tuftsin for its ability to to enhance the chemotactic, bactericidal and phagocytic activities of polymorphonuclear leukocytes (PMN). Both tuftsin and [delta 3-pro3]- tuftsin elicited a similar significant chemotactic effect at a concentration of 10 micrograms/ml. A slight suppression of the chemotactic activity was observed with tuftsin at 10(-3) micrograms/ml and with [delta 3-pro3]-tuftsin at concentrations of 10(-3), 10(-2) (significant) and 10-1 micrograms/ml. Although similar bactericidal activities were observed for both peptides, PMN exposed to [delta 3-pro 3]-tuftsin exhibited increased phagocytic indicies 2-4 times that of tuftsin-treated PMN at concentrations of 0.4, 0.6 and 1.0 microgram/ml.

'Molecular sandwiches' as a basis for structural and functional similarities for interferons, MSH, ACTH, LHRH, myelin basic protein, and albumins

Sequential similarities between the tryptophan peptide of myelin basic protein (residues 111-121), luteinizing hormone releasing hormone, melanotropin, adrenocorticotropin (residues 1-13), human leukocyte interferon (residues 28-40), and various segments of human and bovine serum albumin and hen ovalbumin are presented. It is suggested that these structural similarities may explain observations concerning common functional characteristics such as serotonin modulation, immunological activity with the adjuvant muramyl dipeptide, immunological cross-reactivity, and the possible MSH-ACTH-like activity of a pepsin-derived peptide of interferon.

Specificity of response of intestinal ion transport systems to a pair of natural peptide hormone analogs: somatostatin and urotensin II

Specificity of two intestinal ion transport systems toward the natural peptide hormone analogs somatostatin and urotensin II has been demonstrated by electrophysiological and radiotracer studies in vitro. Somatostatin inhibits active C1 secretion across the theophylline-treated rat colon but urotensin II, a dodecapeptide somatostatin analog from the teleost caudal neurosecretory system, is without effect. Conversely, urotensin II stimulates active Na and C1 absorption across the posterior intestine of the 5% seawater-adapted goby, Gillichthys mirabilis, but somatostatin is ineffective. From these and others' studies, it appears that in both systems, increased net absorption results from increased mucosal-to-serosal unidirectional ion fluxes. Based on structure-activity relationships in these and other systems, it is speculated that the difference in amino acid residues at position 4 (somatostatin-Lys, urotensin II-Ala) may contribute to the observed specificity.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.