Reversible seryl-phosphorylation contributes to the light/dark regulation of C4-leaf phosphoenolpyruvate carboxylase (PEPC) activity in vivo. The specific regulatory residue that, upon in vitro phosphorylation by a maize-leaf protein-serine kinase(s), leads to an increase in catalytic activity and a decrease in malate-sensitivity of the target enzyme has been recently identified as Ser-15 in 32P-phosphorylated/activated dark-form maize PEPC (J-A Jiao, R Chollet [1990] Arch Biochem Biophys 283: 300-305). In order to ascertain whether this N-terminal seryl residue is, indeed, the in vivo regulatory phosphorylation site, [32P]phosphopeptides were isolated and purified from in vivo32P-labeled maize and sorghum leaf PEPC and subjected to automated Edman degradation analysis. The results show that purified light-form maize PEPC contains 14-fold more 32P-radioactivity than the corresponding dark-form enzyme on an equal protein basis and, more notably, only a single N-terminal serine residue (Ser-15 in maize PEPC and its structural homolog, Ser-8, in the sorghum enzyme) was found to be 32P-phosphorylated in the light or dark. These in vivo observations, combined with the results from our previous in vitro phosphorylation studies (J-A Jiao, R Chollet [1989] Arch Biochem Biophys 269: 526-535; [1990] Arch Biochem Biophys 283: 300-305), demonstrate that an N-terminal seryl residue in C4 PEPC is, indeed, the regulatory site that undergoes light/dark changes in phosphorylation-status and, thus, plays a major, if not cardinal role in the light-induced changes in catalytic and regulatory properties of this cytoplasmic C4-photosynthesis enzyme in vivo.相似文献
The CO2/O2 specificity factor of sucrose gradient purified ribulose 1,5-bisphosphate carboxylase/oxygenase from the C3-C4 intermediate plants Moricandia arvensis (79 ± 1) and Panicum milioides (89 ± 2) was similar to the respective values of the enzyme from the closely related C3 species, Moricandia foetida (80 ± 5) and Panicum laxum (86 ± 2). Thus, the kinetic properties of this bifunctional enzyme do not explain the reduced rates of photorespiration exhibited by either of these intermediate species. 相似文献
Tumour necrosis factor (TNF), released by induced macrophages, causes tumour necrosis in animals and kills preferentially transformed cells in vitro. mRNA induced in the established mouse monocytic PU 5.1.8 cell line by lipopolysaccharide, was converted into double-stranded cDNA and cloned in the pAT153 vector. Recombinant plasmids were screened by plus-minus hybridization and TNF-specific oligonucleotide probes constructed on the basis of partial amino acid sequences of rabbit TNF. A series of TNF specific clones were identified and confirmed by hybrid selection of mouse TNF-specific mRNA. The sequence codes for a 235 amino acids long polypeptide, of which 156 amino acids presumably correspond to the mature product. It can be concluded that mature mouse TNF is a glycosylated dimer. Biologically active TNF was secreted by both Cos-I and CHO-cells transfected with the chimaeric expression vector pSV2d2-mTNF containing the coding region of the mouse TNF cDNA gene. 相似文献
The distribution of 14C in photosynthetic metabolites of two naturally occurring higher plants with reduced photorespiration, Moricandia arvensis and Panicum milioides, in pulse and pulse-chase 14CO2 incorporation experiments was similar to that for the C3 species, M. foetida and Glycine max. After 6 seconds of 14CO2 incorporation, only about 6% of the total 14C fixed was in malate and aspartate in both M. arvensis and P. milioides. The apparent turnover of the C4 acids was very slow, and malate accumulated during the day in M. arvensis. Thus, C4 acid metabolism by M. arvensis and P. milioides had no significant role in photosynthetic carbon assimilation under the conditions of our experiments (310 microliters CO2 per liter, 21% O2, 1100 or 1900 micromoles photon per square meter per second, 27°C).
After a 36-second chase period in air containing 270 microliters CO2 per liter, about 20% of the total 14C fixed was in glycine with M. arvensis, as compared to 15% with M. foetida, 14% with P. milioides, and 9% with G. max. After a 36-second chase period in 100 microliters CO2 per liter, the percentage in glycine was about twice that at 270 microliters CO2 per liter in the C3 species and P. milioides, but only 20% more 14C was in glycine in M. arvensis. These data suggest that either the photorespiratory glycine pool in M. arvensis is larger than in the other species examined or the apparent turnover rate of glycine and the flow of carbon into glycine during photorespiration are less in M. arvensis. An unusual glycine metabolism in M. arvensis may be linked to the mechanism of photorespiratory reduction in this crucifer.
Panicum milioides, a naturally occurring species with reduced photorespiration, P. bisulcatum, a C3 species, and P. miliaceum, a C4 species, were grown for 4 weeks at altered pO2 and pCO2 and several vegetative growth parameters were determined at weekly intervals. Compared to a pO2 of 10%, a greater O2 inhibition of the relative growth rate and dry matter production was observed for P. bisulcatum than for P. milioides at both 21% and 40% O2, whereas little effect of O2 was noted for P. miliaceum. Similarly, exposures to elevated pCO2 of 500 and 1000 μ1 CO2/liter resulted in a greater stimulation of vegetative growth for P. bisulcatum than for P. milioides, with little effect on P. miliaceum. The CO2 compensation concentration of P. milioides was less than that of P. bisulcatum over a pO2 range of 5 to 40%. At 5% O2, the compensation concentration was relatively O2-insensitive, whereas above 5% it increased with increasing pO2. It is concluded that P. milioides represents the first well documented example of a C3 plant with reduced photorespiration, based on both leaf CO2 exchange parameters and growth analyses of dry matter production. 相似文献
This paper describes a joint study of the structure and nonlinear optical properties of vacuum evaporated thin films of copper phthalocyanine (CuPc for brevity). Film thickness ranges from 50 to 500 nm. The anisotropic paramagnetic resonance of Cu++ ions reveals that the Pc rings lie almost parallel to the substrate plane with however a large angular distribution (30° FWHM). Third harmonic optical generation measurements performed at 1.064 m and 1.907 m fundamental wavelengths give respectively an average value of the cubic susceptibility (3)(-3,)=(4±0.4)·10–12 e.s.u. and (2.1+-0.2) · 10-12 These values, although significantly higher than for a common ionic crystal, are about one order of magnitude lower than in conjugated 1-D systems, which shows that the 2-D -electron delocalization is less profitable than the 1-D one. Besides third harmonic, we have also observed second harmonic generation. Its polarization dependence is characteristic of a quadratic susceptibility enhanced in one direction, almost perpendicular to the substrate, withdeff comprised between 30 and 60 · 10-9 e.s.u. The possible origins ofdeff are discussed. 相似文献
The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs. 相似文献
Treatment of crystalline tobacco ribulosebisphosphate carboxylase (EC 4.1.1.39) with the arginine-selective α-dicarbonyl, 2,3-butanedione, results in a time- and concentration-dependent loss of activity. Inactivation is markedly enhanced by borate buffer and alkaline pH and is partially reversed upon removal of excess reagent and borate by gel filtration. Of the various ligands examined, only the phosphorylated substrate, ribulosebisphosphate, protects against inactivation. These results suggest an essential role for arginyl residues in the enzymic mechanism of ribulosebisphosphate carboxylase, probably as binding sites for the negatively charged phosphate groups of the non-gaseous substrate. 相似文献