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311.
312.
Magdalena T. Tosteson Michael P. Caulfield Jay J. Levy Michael Rosenblatt Daniel C. Tosteson 《Bioscience reports》1988,8(2):173-183
We have used the chemically synthesized sequence of pre-pro-parathyroid hormone and several of its analogues to test the notion that the capacity of amphipathic peptides to aggregate in membranes and form ion-permeable channels correlates with their ability to function as signal sequences for secreted proteins. We found that pre-pro-parathyroid hormone (the signal sequence and pro-region of parathyroid hormone (M)), as well as some of its analogues, forms aggregates of monomers which are ion-permeable. The ion-permeable aggregates (2–3 monomers) formed by (M) are voltage-dependent and are more permeable for cations than for anions. The compounds which formed ion channels in bilayers also acted as potential signal sequences. We conclude that the ability of peptides to form ion-permeable pathways in bilayers may be correlated to their ability to function as signal peptides. 相似文献
313.
Most proteins located in chloroplasts are encoded by nuclear genes, synthesized in the cytoplasm, and transported into the organelle. The study of protein uptake by chloroplasts has greatly expanded over the past few years. The increased activity in this field is due, in part, to the application of recombinant DNA methodology to the analysis of protein translocation. Added interest has also been gained by the realization that the transport mechanisms that mediate protein uptake by chloroplasts, mitochondria and the endoplasmic reticulum display certain characteristics in common. These include amino terminal sequences that target proteins to particular organelles, a transport process that is mechanistically independent from the events of translation, and an ATP-requiring transport step that is thought to involve partial unfolding of the protein to be translocated. In this review we examine recent studies on the binding of precursors to the chloroplast surface, the energy-dependent uptake of proteins into the stroma, and the targeting of proteins to the thylakoid lumen. These aspects of protein transport into chloroplasts are discussed in the context of recent studies on protein uptake by mitochondria.Abbrevlations CAT
chloramphenicol acetyl transferase
- CCCP
carbonylcyanide m-chlorophenylhydrazone
- DHFR
dihydrofolate reductase
- EPSP
5-enol-pyruvylshikimate-3-phosphate
- ER
endoplasmic reticulum
- LHCP
light harvesting chlorophyll a/b apoprotein
- NPT
neomycin phosphotransferase
- oATP
adenosine-2,3-dialdehyde-5-triphosphate
- P-inorganic phosphate Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- SSU
small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase
- SRP
signal recognition particle 相似文献
314.
Under well-watered conditions in the laboratory, Sedum pulchellum assimilated CO2 only during the day, yet exhibited small nocturnal increases in tissue acid content followed by deacidification in the light (CAM-cycling). When drought-stressed, little CO2 was fixed in the day and none at night, yet even greater acid fluctuations were observed (CAM-idling). Calculations indicate that water savings associated with CAM-cycling when water is available are small. Water saving is more likely to be significant during CAM-idling when water supply is limited and stomata are closed day and night. Thus, in this species, CAM-idling may be of greater benefit to the plant, relative to CAM-cycling, in surviving habitats prone to frequent drought stress.Abbreviations A
CO2 exchange rate
- CAM
Crassulacean acid metabolism
- ci
shoot internal CO2 concentration
- gc
shoot conductance to CO2
- PPFD
photosynthetic photon flux density
- WUE
water-use efficiency
Supported by National Science Foundation Grant No. DMB 8506093. 相似文献
315.
Paul B. M. Joyce David F. Spencer Linda Bonen Michael W. Gray 《Plant molecular biology》1988,10(3):251-262
We have begun a systematic search for potential tRNA genes in wheat mtDNA, and present here the sequences of regions of the wheat mitochondrial genome that encode genes for tRNAAsp (anticodon GUC), tRNAPro (UGG), tRNATyr (GUA), and two tRNAsSer (UGA and GCU). These genes are all solitary, not immediately adjacent to other tRNA or known protein coding genes. Each of the encoded tRNAs can assume a secondary structure that conforms to the standard cloverleaf model, and that displays none of the structural aberrations peculiar to some of the corresponding mitochondrial tRNAs from other eukaryotes. The wheat mitochondrial tRNA sequences are, on average, substantially more similar to their eubacterial and chloroplast counterparts than to their homologues in fungal and animal mitochondria. However, an analysis of regions 150 nucleotides upstream and 100 nucleotides downstream of the tRNA coding regions has revealed no obvious conserved sequences that resemble the promoter and terminator motifs that regulate the expression of eubacterial and some chloroplast tRNA genes. When restriction digests of wheat mtDNA are probed with 32P-labelled wheat mitochondrial tRNAs, <20 hybridizing bands are detected, whether enzymes with 4 bp or 6 bp recognition sites are used. This suggests that the wheat mitochondrial genome, despite its large size, may carry a relatively small number of tRNA genes. 相似文献
316.
317.
318.
Galanin-Like Immunoreactivity Is Unchanged in Alzheimer''s Disease and Parkinson''s Disease Dementia Cerebral Cortex 总被引:1,自引:1,他引:0
M. Flint Beal Ross A. Clevens Geetinder K. Chattha Usha M. MacGarvey Michael F. Mazurek Steven M. Gabriel 《Journal of neurochemistry》1988,51(6):1935-1941
Galanin is a recently isolated neuropeptide that is of particular interest in dementing disorders because of its known colocalization with choline acetyltransferase in magnocellular neurons of the basal nucleus of Meynert. These neurons degenerate in Alzheimer's disease, and there is a corresponding deficiency of cortical choline acetyltransferase activity. In the present study, galanin-like immunoreactivity was measured in the postmortem cerebral cortex and hippocampus of 10 controls and 14 patients who had had Alzheimer's disease. Significant reductions of choline acetyltransferase activity (50-60%) were found in all regions examined; however, there was no significant effect on concentrations of galanin-like immunoreactivity. Similar measurements were made in postmortem tissues of 12 control and 13 demented Parkinsonian patients who had had Alzheimer-type cortical pathology. Choline acetyltransferase activity was again significantly decreased in all regions examined but there were no significant reductions in galanin-like immunoreactivity. Experimental lesions of the fornix in rats produced parallel significantly correlated reductions of both choline acetyltransferase activity and galanin-like immunoreactivity in the hippocampus. Galanin-like immunoreactivity in the human hypothalamus consisted of two molecular-weight species on gel-permeation chromatography, and two forms were resolved by reverse-phase HPLC. The paradoxical preservation of galanin-like immunoreactivity, despite depletion of the activity of choline acetyltransferase, with which it is colocalized, is as yet unexplained. Recent studies have shown that galanin inhibits both acetylcholine release in the hippocampus and memory acquisition; therefore, preserved galanin may exacerbate the cholinergic and cognitive deficits that accompany dementia. 相似文献
319.
Calcium-Dependent Evoked Release of N[3 H]Acetylaspartylglutamate from the Optic Pathway 总被引:2,自引:0,他引:2
Guochuan Tsai Gianluigi Forloni Michael B. Robinson Barbara L. Stauch Joseph T. Coyle 《Journal of neurochemistry》1988,51(6):1956-1959
N-Acetylaspartylglutamate (NAAG) is a neuropeptide localized to several putative glutamatergic neuronal systems, including the rodent optic pathway. To determine whether the peptide is released by depolarization, the superior colliculus of the rat was perfused with 2 microCi of [3H]NAAG, then with Krebs-bicarbonate buffer for 1 h, using a microdialysis system. Subsequently, 10-min fractions were collected and analyzed by HPLC for [3H]NAAG. Addition of 100 microM veratridine resulted in a several-fold increase in the evoked release of [3H]NAAG that was virtually abolished by coperfusion with Ca2+-free Krebs buffer containing 1 mM EGTA. When [3H]glutamate was used as the precursor, veratridine depolarization resulted in only an 80% increase in the release of [3H]NAAG. Prior enucleation of the right eye reduced the spontaneous release of [3H]NAAG by 50%, and the veratridine-evoked release by greater than 85%, from the left superior colliculus. These results suggest that NAAG is released upon depolarization and may serve as a neurotransmitter/neuromodulator in the optic tract. 相似文献
320.
John I. Yoder Joe Palys Kevin Alpert Michael Lassner 《Molecular & general genetics : MGG》1988,213(2-3):291-296
Summary As an initial step towards developing a transposon mutagenesis system in tomato, the maize transposable element Ac was transformed into tomato plants via Agrobacterium tumefaciens. Southern analysis of leaf tissue indicated that in nine out of eleven transgenic plants, Ac excised from the T-DNA and reintegrated into new chromosomal locations. The comparison of Ac banding pattern in different leaves of the same primary transformant provided evidnece for transposition during later stages of transgenic plant development. There was no evidence of Ds mobilization in tomato transformants. 相似文献