Biomedical subjects

S J Paterson

Publications and source records attributed to S J Paterson.

45 records · Page 3Linked to original sources

PubMed1980

Comparison of the binding characteristics of tritiated opiates and opioid peptides.

1 Binding assays on homogenates of guinea-pig brain showed that the maximal number of binding sites was different tritiated ligands interacting with the opiate receptors. 2 At 25 degrees C the binding capacity of morphine or dihydromorphine was only about 3 pmol/g fresh brain whereas etorphine and D-Ala2-L-Leu5- and D-Ala2-L-Met5-enkephalin amide had capacities of 13 to 15 pmol/g brain. D-Ala2-D-Leu5-enkephalin had an intermediate capacity of about 6 pmol/g brain. 3 The binding capacities of the natural methionine- and leucine-enkephalins measured at 0 degrees C were 5 to 6 pmol/g brain. At this temperature, the binding capacity of dihydromorphine, D-Ala2-D-Leu5-enkephalin and of the two enkephalin amides was only slightly lower than at 25 degrees C. 4 In assays in which unlabelled ligand competed with the same labelled ligand, the inhibition constants (KI) were equal to or not more than twice as large as the equilibrium dissociation constant (KD) determined in saturation assays. In contrast, the KI of unlabelled dihydromorphine against [3H]-D-Ala2-D-Leu5-enkephalin or of unlabelled D-Ala2-D-Leu5-enkephalin against [3H]-dihydromorphine was about 20 times higher than the respective KD values. 5 When for a given compound the ratio of the KI value against [3H]-D-Ala2-D-Leu5-enkephalin to the KI value against [3H]-dihydromorphine (discrimination ratio) is calculated, a high value indicates selectivity in favour of the mu-receptor and a low value selectivity in favour of the delta-receptor. The most selective mu-agonist known so far is normorphine with a discrimination ratio of 70 and the most selective delta-agonist is D-Ala2-D-Leu5-enkephalin with a ratio of 0.11. The selectivity of the known antagonists is in favour of the mu-receptor, since their discrimination ratios are larger than 1, varying between 10 for naloxone and 4 for Mr 2266.

Animals↗

PubMed1980

Effects of changes in the structure of enkephalins and of narcotic analgesic drugs on their interactions with mu- and delta-receptors.

1 The activity pattern of analogues of the enkephalins was determined in four parallel assays, the inhibition of the electrically evoked contraction of the guinea-pig ileum and mouse vas deferens at 36 degrees C and the inhibition of [(3)H]-naltrexone and [(3)H]-leucine-enkephalin binding at 0 to 4 degrees C in homogenates of guinea-pig brain.2 The activity pattern was best characterized by the ratio of the potency in the guinea-pig ileum to that in the mouse vas deferens (G.p.i./M.v.d.) and the ratio of the potency in inhibiting [(3)H]-naltrexone binding to that in inhibiting [(3)H]-leucine-enkephalin binding (Nal/Leu).3 The enkephalins had low G.p.i./M.v.d. (0.02 to 0.09) and low Nal/Leu (0.05 to 0.18) ratios whereas the corresponding values for morphine were 7.0 and 7.5.4 Analogues obtained by substituting D-Ala for Gly(2) and D-Met or D-Leu for L-Met(5) or L-Leu(5) showed only minor changes in G.p.i./M.v.d. (0.01 to 0.11) and in Nal/Leu (0.06 to 0.13) ratios.5 Analogues in which resistance to enzymatic degradation was brought about by amidation of the C-terminal carboxylic group or methylation of the amino group of tyrosine or both modifications, had G.p.i./M.v.d. ratios of 1.2 to 5.5 and Nal/Leu ratios of 0.5 to 21. High values (2.1 and 3.4) were found for the potent antinociceptive analogue of Sandoz, Tyr-D-Ala-Gly-NCH(3)Phe-Met(O)-ol.6 In the mouse vas deferens, some of the analogues with high G.p.i./M.v.d. and Nal/Leu ratios were tested for antagonism by naloxone and found to require less than the high concentration needed for the natural enkephalins. C57/BL mice, which have a lowered sensitivity to morphine but a normal response to peptides with low G.p.i./M.v.d. and Nal/Leu ratios, had a lowered sensitivity to analogues with high ratios.7 In the alkaloid-like series of narcotic analgesic drugs, ketobemidone, levorphanol, methadone, etorphine and the antagonist Mr 2266 had lower Nal/Leu ratios (1.0 to 2.8) than morphine, normorphine, naloxone and naltrexone (8 to 12).8 It would appear that compounds with low G.p.i./M.v.d. and Nal/Leu ratios interact mainly with delta-receptors in the brain and peripheral nervous system while compounds with high ratios interact mainly with mu-receptors. For antinociceptive action mu-receptors may be more important than delta-receptors.

Analgesics, Opioid↗

PubMed1979

The amino acid sequence of dihydrofolate reductase from the mouse lymphoma L1210.

The determination of the amino acid sequence of the dihydrofolate reductase (EC 1.5.1.3) from cells of the mouse lymphoma L1210 is described. The protein was cleaved by cyanogen bromide to produce the six fragments CB1 (residues 1 to 14), CB2 (residues 15 to 52), CB3 (residues 53 to 111), CB4 (residues 115 to 125), CB5 (residues 126 to 139), and CB6 (residues 140 to 186). One of the fragments, CB2, contained an internal homoserine derived from a methionine which was not cleaved by cyanogen bromide. The amino acid sequences and order of the cyanogen bromide fragments were determined by a combination of automatic and manual sequence analyses of the fragments and small peptides from tryptic, thermolytic, and Staphylococcus aureus protease digestions. The complete sequence comprises 186 residues in a single polypeptide chain of molecular weight 21,458. Comparison of the sequence of the L1210 dihydrofolate reductase with the sequences of the enzymes from Streptococcus faecium, escherichia coli RT500, and Lactobacillus casei indicates that all enzymes show some homology, which is strongest in the regions forming the substrate binding cleft.

Amino Acid Sequence↗

PubMed1979