Molecular properties of 4-substituted indole-3-acetic acids affecting pea pericarp elongation

Pea (Pisum sativum L.) fruit naturally contain the auxins, indole-3-acetic acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA). However, only 4-Cl-IAA can substitute for the seeds in maintaining pea fruit growth in planta. The importance of the substituent at the 4-position of the indole ring was tested by comparing the molecular properties of 4-X-IAA (X = H, Me, Et, F, or Cl) and their effect on the elongation of pea pericarps in planta. Structure-activity is discussed in terms of structural data derived from X-ray analysis, computed conformations in solution, semiempirical shape and bulk parameters, and experimentally determined lipophilicities and NH-acidities. The size of the 4-substituent, and its lipophilicity are associated with growth promoting activity of pea pericarp, while there was no obvious relationship with electromeric effects.     

Identification of chloroplast signal recognition particle RNA genes

The signal recognition particle (SRP) is a ribonucleoprotein complex responsible for targeting proteins to the ER membrane in eukaryotes, the plasma membrane in bacteria and the thylakoid membrane in chloroplasts. In higher plants two different SRP-dependent mechanisms have been identified: one post-translational for proteins imported to the chloroplast and one co-translational for proteins encoded by the plastid genome. The post-translational chloroplast SRP (cpSRP) consists of the protein subunits cpSRP54 and cpSRP43. An RNA component has not been identified and does not seem to be required for the post-translational cpSRP. The co-translational mechanism is known to involve cpSRP54, but an RNA component has not yet been identified. Several chloroplast genomes have been sequenced recently, making a phylogenetically broad computational search for cpSRP RNA possible. We have analysed chloroplast genomes from 27 organisms. In higher plant chloroplasts, no SRP RNA genes were identified. However, eight plastids from red algae and Chlorophyta were found to contain an SRP RNA gene. These results suggest that SRP RNA forms a complex in these plastids with cpSRP54, reminiscent of the eubacterial SRP.     

Light-induced multistep oxidation of dinuclear manganese complexes for artificial photosynthesis

Two dinuclear manganese complexes, [Mn(2)BPMP(mu-OAc)(2)].ClO(4) (1, where BPMP is the anion of 2,6-bis([N,N-di(2-pyridinemethyl)amino]methyl)-4-methylphenol) and [Mn(2)L(mu-OAc)(2)].ClO(4) (2, where L is the trianion of 2,6-bis([N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2-pyridinemethyl)amino]methyl)-4-methylphenol), undergo several oxidations by laser flash photolysis, using ruthenium(II)-tris-bipyridine (tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate) as photo-sensitizer and penta-amminechlorocobalt(III) chloride as external electron acceptor. In both complexes stepwise electron transfer was observed. In 1, four Mn-valence states from the initial Mn(2)(II,II) to the Mn(2)(III,IV) state are available. In 2, three oxidation steps are possible from the initial Mn(2)(III,III)state. The last step is accomplished in the Mn(2)(IV,IV) state, which results in a phenolate radical. For the first time we provide firm spectral evidence for formation of the first intermediate state, Mn(2)(II,III), in 1 during the stepwise light-induced oxidation. Observation of Mn(2)(II,III) is dependent on conditions that sustain the mu-acetato bridges in the complex, i.e., by forming Mn(2)(II,III) in dry acetonitrile, or by addition of high concentrations of acetate in aqueous solutions. We maintain that the presence of water is necessary for the transition to higher oxidation states, e.g., Mn(2)(III,III) and Mn(2)(III,IV) in 1, due to a bridging ligand exchange reaction which takes place in the Mn(2)(II,III) state in water solution. Water is also found to be necessary for reaching the Mn(2)(IV,IV) state in 2, which explains why this state was not reached by electrolysis in our earlier work (Eur. J. Inorg. Chem (2002) 2965). In 2, the extra coordinating oxygen atoms facilitate the stabilization of higher Mn valence states than in 1, resulting in formation of a stable Mn(2)(IV,IV) without disintegration of 2. In addition, further oxidation of 2, led to the formation of a phenolate radical (g = 2.0046) due to ligand oxidation. Its spectral width (8 mT) and very fast relaxation at 15 K indicates that this radical is magnetically coupled to the Mn(2)(IV,IV) center.     

Pharmacokinetic investigation of a 14C-labelled beta 3/alpha tetrapeptide in rats

The solid-phase synthesis and an ADME investigation with albino and pigmented male rats of the doubly 14C-labelled beta/alpha-tetrapeptide derivative Ac-beta3 hTyr-(D)Trp-beta3 hLys-beta3 hThr-lactone (3; Fig. 3) are described. After intravenous (i.v.) and peroral (p.o.) administration of the peptide, its concentration in blood and plasma, its tissue distribution, and the metabolism and the excretion of the peptide were analyzed over a period of up to 7 days post dose. The tetrapeptide in its ring opened form, 5, has a bioavailability of ca. 25%; radioactivity is distributed in the animals in an organ-specific way, and the compound appears to pass the blood-brain barrier to a very small extent, if at all (Tables 1-3 and Figs. 2-6). Excretion (37% renal, 44% fecal, including biliary) of the tetrapeptide 4 days after i.v. administration is almost complete, with only 4.3% remaining in the carcass; 4 days after p.o. administration 97% of the dose has been excreted in the feces. Radiochromatograms taken of plasma (0.5 and 24 h after i.v. dosing) and of urine and feces extracts (0-48 h collected) reveal the presence of lactone 3 and/or the corresponding hydroxy acid 5 with essentially no or very minor other peaks, respectively, representing possible metabolites (Tables 4-6, and Fig. 7 and 8). A comparison with a previous ADME investigation of a beta-nonapeptide show that--except for the lack of metabolism--all aspects of exposure, distribution, and elimination are different (structure-specific properties). The investigated tetrapeptide 3 is a potent and highly specific agonist of the somatostatin receptor hsst4, rendering the results described herein promising for diagnostic and therapeutic applications of beta-peptides.