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C McMartin

Publications and source records attributed to C McMartin.

At least 55 records · Page 3Linked to original sources
PubMed1974

The isolation and amino acid sequence of an adrenocorticotrophin from the pars distalis and a corticotrophin-like intermediate-lobe peptide from the neurointermediate lobe of the pituitary of the dogfish Squalus acanthias.

An adrenocorticotrophic hormone (ACTH) was isolated from extracts of the pars distalis of the pituitary of the dogfish Squalus acanthias by gel filtration and ion-exchange chromatography. It had 15% of the potency of human ACTH in promoting cortico-steroidogenesis in isolated rat adrenal cells. Sequence analysis revealed it to be a nonatria-contapeptide with the following primary structure: Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Met-Gly-Arg-Lys-Arg-Arg-Pro-Ile-Lys-Val-Tyr-Pro-Asn-Ser-Phe-Glu-Asp-Glu-Ser-Val-Glu-Asn-Met-Gly-Pro-Glu-Leu. The N-terminal tridecapeptide sequence was identical with the proposed structure of dogfish alpha-melanocyte-stimulating hormone (alpha-MSH). On comparison with human ACTH eleven amino acid differences were seen, nine of which are in the 20-39 region of the molecule which is not essential for the steroidogenic activity of ACTH. A peptide identical with the 18-39 portion of this new ACTH was similarly isolated from the neurointermediate lobe of the pituitary where considerable amounts of dogfish alpha-MSH were found. This supported our view that ACTH as well as having a distinct biological role of its own is also the precursor of alpha-MSH.

Adrenal Cortex Hormones↗
PubMed1974

Structural studies of alpha-melanocyte-stimulating hormone and a novel beta-melanocyte-stimulating hormone from the neurointermediate lobe of the pituitary of the dogfish Squalus acanthias.

A melanocyte-stimulating hormone (MSH) has been isolated from extracts of the neurointermediate lobe of the pituitary of the dogfish Squalus acanthias by gel-filtration and ion-exchange chromatography. It had approximately 1% of the potency of mammalian alpha-MSH on bioassays in vitro on frog skin and dogfish skin. Sequence analysis revealed it to be a hexadecapeptide with the following primary structure: Asp-Gly-Asp-Asp-Tyr-Lys-Phe-Gly-His-Phe-Arg-Trp-Ser-Val-Pro-Leu. It appears to be related to the beta-MSH species of mammalian species but has only the sequence -His-Phe-Arg-Trp- in common with the heptapeptide core -Met-Glu-His-Phe-Arg-Trp-Gly- which is characteristic not only of the MSH peptides but also of the adrenocorticotrophins and lipotrophins studied so far. An alpha-MSH was also isolated, 50% of which was amidated at the C-terminus group. Sequence data from this study taken in conjunction with those from a previous study (Lowry & Chadwick, 1970b) revealed it to be a tridecapeptide which is identical with the N-terminal sequence of dogfish adrenocorticotrophin.

Adrenocorticotropic Hormone↗
PubMed1974

Measurement of the dynamics of stimulation and inhibition of steroidogenesis in isolated rat adrenal cells by using column perfusion.

Isolated adrenal cells were perfused in a small column by using Bio-Gel polyacrylamide beads as an inert supporting matrix, and the time-course of the response to various stimuli was observed by measuring fluorogenic 11-hydroxycorticosteroids in the effluent. A small but significant response was observed 1 min after stimulation with physiological concentrations of ACTH (adrenocorticotrophin), but the response did not start to build up rapidly for 3-4min and eventually reached a plateau after 9-10min. A similar pattern of events was observed for the decay of the steroid output on removal of ACTH. ACTH analogues, including one with a long duration of action in vivo, were found to produce responses with similar kinetics. However, cyclic AMP caused a more rapid increase in steroidogenesis and its effects were more short-lived after withdrawal. If, as present evidence suggests, cyclic AMP is produced rapidly after ACTH stimulation the delayed build-up of the steroidogenic response to ACTH would indicate that cyclic AMP may not be the intracellular mediator. When inhibitors were applied during ACTH stimulation, aminoglutethimide, which blocks mitochondrial conversion of cholesterol into pregnenolone (3beta-hydroxypregn-5-en-20-one), caused a rapid fall in steroid output (1 min), whereas cycloheximide took longer to achieve its full effect. Nevertheless, the response had fallen by 50% in 2 min, indicating a much shorter half-life than that previously reported for the labile protein implicated in steroidogenesis. In addition the rapid response to cyclic AMP makes it unlikely that steroid production is induced as a result of initiation of protein synthesis. This suggests that the labile protein plays an obligatory but permissive role in the development of the response. Column perfusion has proved to be a simple technique which can readily yield accurate data on responses of cells to stimulants and inhibitors.

Acrylamides↗
PubMed1973

Pituitary peptide.

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Adrenocorticotropic Hormone↗
PubMed1973

Confirmation of the 1-20 amino acid sequence of human adrenocorticotrophin.

The tryptic fragments of natural human adrenocorticotrophin, were separated by countercurrent distribution and a correction in positions 25, 26, 27 and 30 was made by Riniker et al. (1972) in a study of the fragment containing residues 22-39. We have purified the remaining tryptic fragments, namely residues 1-8, 9-15, 16-21 and 17-21, by using ion-exchange chromatography on CM-cellulose and have carried out sequence determination by using the subtractive Edman degradation procedure and digestion with aminopeptidase M and carboxypeptidase B. These results have confirmed the proposed sequence for human adrenocorticotrophin in regions 6-7, 10-14 and 17-20, which had previously been arrived at only by analogy with the invariant sequence found in the three other mammalian adrenocorticotrophin species that had been investigated.

Adrenocorticotropic Hormone↗
PubMed1972

Complete amino acid analysis of peptides and proteins after hydrolysis by a mixture of sepharose-bound peptidases.

Incubation with a mixture of Sepharose-bound peptidases was shown to result in the quantitative release of amino acids from certain peptides and S-aminoethylated proteins. Subtraction of the low background values of amino acids generated by the enzymes enables amino acid ratios of corticotrophin-(1-24)-tetracosapeptide to be determined with a standard deviation on repeat digestions of 3-5%. Good values were obtained for amino acids that are completely or partially destroyed on acid hydrolysis, i.e. tryptophan, tyrosine, serine, asparagine and glutamine. Experiments with peptides containing d-amino acids showed that the enzyme mixture is stereospecific and could therefore be used to detect the presence of d-residues in peptides. The enzyme mixture completely hydrolyses peptide fragments obtained after Edman degradation and should therefore be useful for determining sequences of peptides containing acid-labile amino acid residues. The activities of the bound enzymes were unaltered over a period of 7 months and they provide a simple, reproducible procedure for the quantitative determination of amino acids in peptides and proteins containing l-amino acids.

Adrenocorticotropic Hormone↗
PubMed1972

Isolation and identification of pharmacologically active amino acids in skin and their structure-activity relationship on the guinea-pig ileum.

1. Aqueous extracts of stratum corneum were found to cause histamine-like contractions of the guinea-pig ileum which were not antagonized by mepyramine, atropine or bromolysergic acid diethylamide.2. The compounds responsible for this contraction were isolated by chromatography and shown to be common amino acids, particularly L-serine and L-alanine which occur in abundance in the stratum corneum.3. Amino acid analogues were assayed on the guinea-pig ileum against alanine as standard. With the exception of gamma-amino butyric acid and L-alanine benzyl ester all analogues which had appreciable activity gave dose-response curves parallel to L-alanine.4. The response to L-alanine benzyl ester was abolished by mepyramine and this analogue appears to be a partial agonist on the histamine receptor.5. The effects of substitution on the equipotent molar ratios of amino acid analogues indicate that all four chemical groups attached to the alpha-carbon of L-alanine interact with the receptor.6. Our results suggest that the guinea-pig ileum contains an L-alpha-amino acid receptor.

Alanine↗