[Receptor selectivity profile of short enkephalin analogs containing D-ornithine at the second position of the molecule]. / Issledovanie profilia retseptornoi selektivnosti ukorochennykh analogov énkefalina, soderzhashchikh D-ornitin vo vtorom polozhenii molekuly.

The radioreceptor binding assay using a membrane fraction from the rat brain was applied to study binding activity and opiate receptor selectivity of truncated enkephalin analogs (with a free or modified C-terminal carboxyl group) bearing D-ornithine at the second position. D-ornithine introduction does not lead to the increase of mu-receptor selectivity as is proposed by the Schwyzer membrane selection model. Some additional modifications (C-terminal amidation or ornithine side chain acetylation) of tetrapeptide molecule were required to reach mu-selectivity. Simultaneous replacement of glycine by D-ornithine and C-terminal carboxyl amidation resulted in the potent analog whose selectivity toward the mu-receptors was 113 times as high as that of leucine-enkephalin. D-ornithine side chain prolongation by means of the attachment of some amino acid residues (methionine, leucine, proline, asparagine) led to the original branched enkephalin analogs. Studies of their binding activity showed that the best branched analog was only 27 times more selective for mu-vs delta-opiate receptors.

[The effect of modification of the carboxyl group in short D-arginine 2-containing enkephalin analogs on their affinity and selectivity for opiate receptors]. / Vliianie modifikatsii karboksil'noi gruppy ukorochennykh D-arginin 2-soderzhashchikh analogov énkefalina na ikh srodstvo i izbiratel'nost' k opiatnym retseptoram.

Radioreceptor binding assay using a membrane fraction from the rat brain was applied to study [D-Arg2, Leu5] enkephalin and two series of its analogues truncated at the C-terminus with a free or modified carboxyl group: tetra- and tripeptide amides and ethyl esters. The affinity to mu-specific opiate receptor subtype of the N-terminal [D-Arg2] tetrapeptide ethyl ester was 44 times as high as that of the tripeptide with a free carboxyl, and thus the ester retained up to 10% of leucine-enkephalin binding potency. However, a comparable esterification of the carboxyl group in the N-terminal [D-Arg2] tripeptide led to a 6-fold reduction in its affinity to mu-receptors. Consequently, identical modifications of the C-terminal carboxyl group in enkephalin analogues of various length can have completely different effects. Substitution of the natural glycine residue by D-arginine residue in position 2 of the enkephalin molecule truncated at the C-terminus increased the mu-receptor binding potency of the tetrapeptide, whereas its delta receptor binding potency declined by more than one order of magnitude. Simultaneous replacement of glycine2 by D-arginine2 and carboxyl amidation resulted in the short enkephalin analogue Tyr--D--Arg--Gly--Phe--NH2, whose affinity to mu receptors was four times as high as that of leucine--enkephalin, the tetrapeptide being 284 times more selective for the mu vs. delta opiate receptors.

[Structural-functional relations of short analogs of enkephalin]. / Strukturno-funktsional'nye vzaimootnosheniia korotkikh analogov énkefalina.

The similarity of action of narcotic analgesics and opioid peptides is due to activation of a common opiate receptor as the primary step in initiating biochemical chains responsible for diverse morphine-like effects. The most widely used assays for opioid and analgesic activities are presented and evaluated. Approximately 180 short enkephalin analogues (di-, tri- and tetrapeptides), described in the literature, are systematized and their opioid and systemic analgesic activities compared with methionine-enkephalin and morphine as the reference compounds, respectively. The analysis of structure-opioid activity relationships among these enkephalin analogues substantiates the hypothesis that only a limited N-terminal region of the peptide molecule is essential for the binding of opioid peptides to the subclass of opiate receptors interacting with narcotic alkaloids (mu-receptors). An attempt has been made to identify minimal structural elements responsible for the mu-receptor activation. Shortening of the molecule and modification of its elements are examined with regard to the mu- and delta-receptor selectivity. It is emphasized that the aromatic structure of the C-terminal region of the peptide is not obligatory for the mu-receptor binding. Modifications of short enkephalin analogues which might confer them antagonistic properties are reviewed. The correlation between the ability of short enkephalin analogues to interact with mu-receptors and their antinociceptive properties is discussed along with some structural features pertinent to the analgesic effect after systemic administration of peptides. On the basis of this analysis, peptides containing no more than four amino acids are considered as the most probable morphine-like analgesics.

[Synthesis and biological activity of a lysine-containing cyclic analog of [Leu5]enkephalin]. / Sintez i biologicheskaia aktivnost' lizinsoderzhashchego tsikloanaloga [Leu5]énkefalina.

The cyclic analogue of [Leu5]enkephalin--cyclo (Lys-Tyr-Gly-Gly-Phe-Leu) and two corresponding linear hexapeptides with lysine residue attached to the N- or C-terminus of the molecule have been synthesized by classical methods of peptide chemistry. The addition of lysine residue to the N-terminus of cyclization of the molecule reduce the interaction of these analogues with both central and peripheral opiate receptors. The addition of lysine residue to the C-terminus of the molecule through the epsilon-amino group does not affect the interaction of the analogue with mu-receptors but reduces approximately tenfold its affinity for delta-receptors. All three analogues have analgesic potency similar to that of [Leu5]enkephalin as assayed after intracisternal administration to mice.

Chronic vomiting in a case of citrullinaemia detected after treatment by total parenteral nutrition.

We report a case of a 56 year old woman who presented with a long history of chronic attacks of vomiting. On admission to hospital she was cachectic, and attempted parenteral nutrition induced coma. The illness was found to be due to citrullinaemia, a metabolic disorder of the urea cycle. Our patient is the oldest with this disorder so far described in the literature. The main points of the case and its investigation are outlined: hyperammonaemia, amino acid chromatogram, measurement of enzyme activity in skin and liver biopsy material. The therapeutic measures which led to cure are of particular interest.

[Preparation of RNAase-free E. coli ribosomes active in initiation of protein biosynthesis]. / Vydelenie aktivnykh v initsiatsii biosinteza belka ribosom E. coli, svobodnykh ot primesei RNKaz.

The level of contaminating RNAases in the main components of the protein biosynthesis initiation system, the initiation factors and ribosomes of E. coli, was studied. It was shown that the ribosomes are the major source of contaminating RNAases. A simple procedure for purification of ribosomes active in initiation including Sephadex G-200 gel-filtration of unwashed ribosomes in a 1.5 M NH4Cl-containing buffer was developed.

Action of secretagogues on amylase release from dog pancreatic acini.

This work describes a new preparation of dog pancreatic acini which were used to study amylase release in response to various secretagogues. Neither secretin nor vasoactive intestinal peptide stimulated amylase release from acini. Caerulein, carbachol and human synthetic gastrin G17 stimulated amylase release with the same efficacy, but with different potencies. Bombesin nonapeptide did not show any evidence of a direct stimulatory effect on amylase release. These species-related peculiarities stress the necessity of using the same species when comparing pancreatic cell behaviour in vivo and in vitro.

[MS2 RNA hydrolysis by snake venom phosphodiesterase and template properties of RNA produced by limited exonucleolytic action]. / Gidroliz RNK faga Ms2 fosfodiesterazoi zmennogo iada i matrichnye svoistva RNK-produkta ogranichennogo ekzonukleoliticheskogo deistviia

The action of snake venom phosphodiesterase on bacteriophage MS2 RNA under conditions of limited hydrolysis has been studied. The content of 5'-mononucleotides released during hydrolysis does not correspond to the calculated one based on the 3'-terminal nucleotide sequence of MS2 RNA. This finding suggests the occurrence of endonucleolytic splits in MS2 RNA with concomitant exonucleolytic digestion of some newly formed fragments. A high molecular weight RNA fraction, comprising unfragmented MS2 RNA with about 5-63'-terminal nucleotides removed is separated by sucrose gradient centrifugation and shown not to differ from the native MS2 RNA in its template function in a cell-free protein synthesizing system. It is demonstrated that template activity, polarity of translation, and nascent peptide chain termination on the MS2 replicase cistron are not affected by the removal of 3'terminal nucleotides of MS2 RNA. Consequently, these nucleotides are unessential in translation of native MS2 RNA.