Synthesis and biological activity of linear and cyclic enkephalins modified at the Gly3-Phe4 amide bond

As part of our continuing effort to define structure-activity relationships for enkephalin and design enzymatically resistant analogs, we report the synthesis and biological activities of linear and cyclic enkephalin analogs modified at the Gly3-Phe4 amide bond. The partial retro-inverso enkephalin analog Tyr-D-Ala-gGly-(R,S)-mPhe-Leu-NH2 and its cyclic counterpart, Tyr-cyclo[D-A2 bu-gGly-(R,S)-mPhe-Leu-], were synthesized as diastereomeric mixtures using solution methodology. The racemic benzylmalonate allowed the linear analog to be synthesized by fragment coupling at the reversed bond. Cyclization of the second analog was carried out at high concentration, eliminating formation of polymer by the use of an insoluble base. All gem-diaminoalkyl residues were prepared by conversion of peptidyl amides with benzene iodonium bis(trifluoroacetate). Diastereomers of both compounds were separable by reverse phase HPLC but those of the linear compound racemized rapidly under conditions of testing and were therefore tested together. All analogs tested had activities ranging from 6 to 14% of the activity of Leu enkephalin, indicating that the Gly3-Phe4 amide bond is important, though not crucial, for receptor binding.     

Über eine besondere Art von Laubfall bei einigen immergrünen Holzgewächsen

Ohne Zusammenfassung     

Analysis of mitochondrial DNA from somatic hybrid cell lines of Saccharum officinarum (sugarcane) and Pennisetum americanum (pearl millet)

Mitochondrial DNA (mtDNA) from cell suspension cultures of two intergeneric somatic hybrids of Pennisetum americanum (pearl millet) + Saccharum officinarum (sugarcane) was examined by restriction endonuclease digestion and hybridization with sorghum mtDNA cosmids. The mtDNA of one somatic hybrid was indistinguishable from that of pearl millet, while the second exhibited a combination of parental mtDNAs, suggesting mitochondrial fusion. Several novel, possibly recombinant, mtDNA restriction fragments were detected in this hybrid, which may have resulted from intergenmic recombination.Florida Agriculture Experiment Station Journal Series No: 8090.     

The contribution of abiotic processes to buried litter decomposition in the northern Chihuahuan desert

Summary Creosobebush (Larrea tridentata) fine litter was treated with either the general biocide HgCl₂ and CuSO₄ or water (controls) and buried 5 cm beneath the soil surface in the northern Chihuahuan Desert. The treated litter showed significantly less mass loss than controls during the three month summer-autumn field study; controls lost about 20% of the original mass while treated litter lost less than 2%. In addition, the total nitrogen content of the control litter increased from an initial concentration of about 14.08 g kg^-1 to 17.62 g kg^-1 dry weight by the end of the study, while treated litter nitrogen content decreased to 13.30 g kg^-1. Results suggest abiotic processes other than leaching have little effect on the decomposition of buried litter in this environment.     

Wheat dwarf virus, a geminivirus of graminaceous plants needs splicing for replication.

By analysing mRNAs with the polymerase chain reaction (PCR) and by studying in vitro generated mutants we have identified an intron in the genome of wheat dwarf virus (WDV), a geminivirus of cereals. Polypeptides whose expression is essential for the replication of the viral DNA have been defined. They are encoded by two distinct overlapping open reading frames (ORFs). The joining of these two ORFs by deletion of the intron as well as the introduction of a frameshift mutation within the intron do not prevent replication of the viral genome in suspension culture cells. In contrast to WDV, the geminiviruses of dicotyledonous plants possess a single continuous ORF, highly homologous to the two individual ones of WDV. We propose that mRNA splicing is a common feature of all geminiviruses of the Gramineae and might contribute to their host class specificity. The existence of a functional intron is a novel finding for the plant viruses.     

Assembly of the barley light-harvesting chlorophyll a/b proteins in barley etiochloroplasts involves processing of the precursor on thylakoids

A barley gene encoding the major light-harvesting chlorophyll a/b-binding protein (LHCP) has been sequenced and then expressed in vitro to produce a labelled LHCP precursor (pLHCP). When barley etiochloroplasts are incubated with this pLHCP, both labelled pLHCP and LHCP are found as integral thylakoid membrane proteins, incorporated into the major pigment-protein complex of the thylakoids. The presence of pLHCP in thylakoids and its proportion with respect to labelled LHCP depends on the developmental stage of the plastids used to study the import of pLHCP. The reduced amounts of chlorophyll in a chlorophyll b-less mutant of barley does not affect the proportion of pLHCP to LHCP found in the thylakoids when import of pLHCP into plastids isolated from the mutant plants is examined. Therefore, insufficient chlorophyll during early stages of plastid development does not seem to be responsible for their relative inefficiency in assembling pLHCP. A chase of labelled pLHCP that has been incorporated into the thylakoids of intact plastids, by further incubation of the plastids with unlabelled pLHCP, reveals that the pLHCP incorporated into the thylakoids can be processed to its mature size. Our observations strongly support the hypothesis that after import into plastids, pLHCP is inserted into thylakoids and then processed to its mature size under in vivo conditions.