Alvin N. Starratt

Isolation of proctolin, a myotropic peptide, from Periplaneta americana

Abstract The isolation of a myotropic substance, proctolin , associated with the innervation of the viscera of the cockroach, Periplaneta americana , is reported. Proctolin, previously described as a neurotransmitter or neurohormone, is a small basic peptide with an estimated molecular weight of 500 to 700. The proctodeal (hindgut) muscles of P. americana contract at threshold levels of about 0·5 ng/ml, equivalent to about 10 −9 M proctolin. Approximately 180 μg proctolin were isolated from 125 kg of whole cockroaches. The isolated peptide was homogeneous on paper and thin-layer chromatography and on high-voltage paper electrophoresis at pH 3·5 and 6·4.

Rebaudioside F, a diterpene glycoside from Stevia rebaudiana

The sweet diterpenoid glycoside, rebaudioside F, was isolated from leaves of a high rebaudioside C producing line of Stevia rebaudiana, and its structure was established by chemical and spectral studies.

New observations on the secondary chemistry of world Ephedra (Ephedraceae)

For several millennia, stem extracts of Ephedra (Ephedraceae, Gnetales) have been used as folk medicines in both the Old and New World. Some species were used in treatments of questionable efficacy for venereal disease in North America during the last century. Many Eurasian species produce phenylethylamine alkaloids, mostly ephedrine and pseudoephedrine, that interact with adrenergic receptors in the mammalian sympathetic nervous system. Asian Ephedra have been used recently in the clandestine manufacture of a street drug, methamphetamine. Although ephedrine alkaloids are not detectable in New World species of Ephedra, together with Asian species they contain other nitrogen-containing secondary metabolites with known neuropharmacological activity. Many mesic and particularly xeric species worldwide accumulate substantial amounts of quinoline-2-carboxylic acids, or kynurenates, in their aerial parts. Many species of Ephedra accumulate cyclopropyl amino acid analogues of glutamate and proline in their stems and roots, and particularly in the seed endosperm. Mesic species synthesize substantial amounts of three L-2-(carboxycyclopropyl)glycine stereomers rarely seen in nature. A cyclopropyl analogue of proline with known antimicrobial activity, cis-3,4-methanoproline, is found in large amounts in the stems and seeds of many Ephedra species. The ability to synthesize cyclopropyl amino acids may be an ancestral feature in the taxon. The natural function in the taxon of these three groups of secondary compounds remains to be established.

Regulation of enzymic oxidation of indole-3-acetic acid by phenols: Structure-activity relationships

Abstract Mono- and diphenols were tested for their effects on the decarboxylation of [1- 14 C]IAA catalysed by purified horseradish peroxidase (EC 1.11.1.7) in the presence or absence of 2,4-dichlorophenol (DCP). The number of hydroxyl groups and their position relative to each other and the nature and position of other substituents on the aromatic ring were found to affect the activity. Although the effects were complex, the following generalizations may be made. (1) Monophenols produce activation when no other cofactor is present. p -Substituted monophenols are more active than o - or m -compounds. In the presence of DCP, the activity varies from slight activation to strong inhibition. (2) m -Diphenols also produce activation in the absence of other cofactors while o - and p -diphenols, with the exception of 3,4-dihydroxyacetophenone and 3,4-dihydroxypropiophenone, produce strong inhibition in the presence or absence of DCP. The o -diphenolsare degraded in the IAA-oxidizing enzyme system and thus produce only a temporary inhibition. (3) m -Diphenols and 3,4-dihydroxyacetophenone produce a sustained inhibition in the presence of DCP. (4) Substitution at position 2 significantly alters the activity of m -diphenols. (5) O -Methylation alters the activity of most o -diphenols. In the absence of DCP, o -methoxyphenols and certain other phenols such as 3,4-dihydroxyacetophenone and 2,6-dihydroxyacetophenone either promote or inhibit IAA oxidation depending on concentration.

Analogs of the insect myotropic peptide proctolin: Synthesis and structure-activity studies

Summary Fifteen pentapeptides structurally related to the insect myotropic substance proctolin synthesized by solution methods were assayed for proctolin activity on cockroach proctodeal muscle. [Phe( p -OMe)2]-Proctolin was almost three times as potent as the natural pentapeptide; other analogs ranged from 15% as active to almost inactive. Related shorter chain-length peptides had little or no activity. None of the synthetic peptides acted as antagonists.

A single receptor transduces both inhibitory and stimulatory signals of FMRFamide-related peptides

In the oviduct of Locusta migratoria, an inhibitory neuropeptide, PDVDHVFLRFamide (SchistoFLRFamide) has separate binding and activation regions. VFLRFamide is the minimum sequence required for binding, which is comparable to the parent peptide, whereas the His residue, which does not contribute to binding, is a critical amino acid for the inhibitory activity of the receptor. In this study, the His residue of HVFLRFamide was substituted by Tyr, Leu, Ile, or Val to yield a group of HVFLRFamide analogues. As revealed by bioassay, all of these hexapeptide analogues exert stimulatory effects on oviduct muscle contraction. However, results from three sets of binding experiments indicate that these stimulatory FMRFamide-related peptides (FaRPs) share the same binding site as PDVDHVFLRFamide and HVFLRFamide, the inhibitory FaRPs. First, unlabeled stimulatory FaRPs competitively displace bound [125I]YDVDHVFLRFamide. Second, two binding sites for the stimulatory peptide YVFLRFamide were identified and both of them have similar binding affinities and maximum binding capacities as the two binding sites for PDVDHVFLRFamide. Third, unlabeled PDVDHVFLRFamide and HVFLRFamide competitively displace the bound [125I]YVFLRFamide in the same manner as unlabeled YVFLRFamide. These findings suggest the presence of a novel ligand-receptor reaction system. In this system, inhibitory peptides and stimulatory peptides share a single receptor by having the same binding sequence VFLRFamide, but are able to produce opposite muscle responses due to differences in activation sites. Correspondingly, this single receptor could be coupled with two different intracellular signaling systems to mediate either inhibitory or stimulatory responses.

Effect of 3,4-dihydroxyacetophenone and some related phenols on the peroxidase-catalysed oxidation of indole-3-acetic acid

Abstract 3,4-Dihydroxyacetophenone, 3,4-dihydroxypropiophenone and acetovanillone differed in activity in the enzymic oxidative reaction of indole-3-acetic acid

Quinoline-2-carboxylic acids from Ephedra species

Abstract A new quinoline-2-carboxylic acid, 4-hydroxy-6-methoxyquinoline-2-carboxylic acid (6-methoxy-kynurenic acid), has been isolated from Ephedra pachyclada ssp. sinaica . Kynurenic and 6-hydroxykynurenic acids, previously reported from plants, were also isolated from Ephedra .

Four cyclopropane amino acids from Ephedra

Abstract Three diastereomers of 2-(carboxycyclopropyl)glycine and cis -3,4-methanproline have been isolated from Ephedra species. This is first report of the natural occurrence of (2 S ,3 R ,4 S )-2-(carboxycyclopropyl)glycine.

Inhibition of conjugation of indole-3-acetic acid with amino acids by 2,6-dihydroxyacetophenone in Teucrium canadense

Abstract 2,6-Dihydroxyacetophenone and five structurally related compounds were tested for their effects on metabolism of[2- 14 C]IAA in stem segments of 3-week-old American germander ( Teucrium canadense ). Pre-treatment of the plants with 2 mM 2,6-dihydroxyacetophenone for 12 hr significantly reduced the formation of two radioactive metabolites, which were tentatively identified as N -(indole-3-acetyl)- L -aspartic acid and N -(indole-3-acetyl)- L -glutamic acid. The chemical pre-treatment also decreased the level of a less polar metabolite chromatographically indistinguishable from oxindole-3-acetic acid, an oxidative product of IAA, and other unidentified metabolites of IAA. Concomitantly, the level of free [2- 14 C]IAA increased significantly in the treated tissue. 2,4-, 2,5- and 3,4-Dihydroxyacetophenones, as well as 3-bromo-2,6-dihydroxyacetophenone and 2-hydroxy-6-methoxyacetophenone, did not show a similar effect.