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31.
In intact, uncoupled type B chloroplasts from spinach, added ATP causes a slow light-induced decline () of chlorophyll a fluorescence at room temperature. Fluorescence spectra were recorded after fast cooling to 77 K and normalized with fluorescein as an internal standard. Related to the fluorescence quenching at room temperature, an increase in Photosystem (PS) I fluorescence (F735) and a decrease in PS II fluorescence (F695) were observed in the low-temperature spectra. The change in the ratio was abolished by the presence of methyl viologen. Fluorescence induction at 77 K of chloroplasts frozen in the quenched state showed lowered variable (Fv) and initial (F0) fluorescence at 690 nm and an increase in F0 at 735 nm. The results are interpreted as indicating an ATP-dependent change of the initial distribution of excitation energy in favor of PS I, which is controlled by the redox state of the electron-transport chain and, according to current theories, is caused by phosphorylation of the light-harvesting complex. 相似文献
32.
W A Murphy V A Lance J Sueiras-Diaz D H Coy 《Biochemical and biophysical research communications》1983,112(2):469-474
Synthetic human pancreatic growth hormone-releasing factor containing 40 amino acids ([hpGRF (1-40)]-OH) significantly stimulated plasma growth hormone (GH) levels in both sodium pentobarbital and urethane anesthetized rats. Synthetic secretin, gastric inhibitory polypeptide (GIP), and glucagon significantly decreased plasma GH levels while synthetic vasoactive intestinal peptide (VIP) had no effect. Secretin and GIP also altered the in vivo plasma GH response to [hpGRF(1-40)]-OH. Whether this effect is the result of an interaction at the pituitary level or is due to an extra-pituitary effect of secretin and GIP awaits further study. 相似文献
33.
The rise time, of Signal IIf and the decay time of P-680+ have been measured kinetically as a function of pH by using EPR. The Photosystem II-enriched preparations which were used as samples were derived from spinach chloroplasts, and they evolved oxygen before Tris washing. The onset kinetics of Signal IIf are in agreement, within experimental error, with the fast component of the decay of an EPR signal attributable to P-680+. The signal IIf rise kinetics also show good agreement with published values of the pH dependence of the decay of P-680+ measured optically (Conjeaud, H. and Mathis, P. (1980) Biochim. Biophys. Acta 590, 353–359). These results are consistent with a model where the species Z (or D1) responsible for Signal IIf is the immediate electron donor to P-680+ in tris-washed Photosystem II fragments. 相似文献
34.
Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP oxidoreductase, EC 1.1.1.49) has been purified to electrophoretic homogeneity from pea chloroplasts. The enzyme, which has a Stokes radius of 52 Å, is a tetramer made up of four 56000 Da monomers. The pH optimum is around 8.2. The enzyme is absolutely specific for NADP. The apparent Km(NADP) is 2.4 ± 0.1 μM. NADPH inhibition of the enzyme is competitive with respect to NADP (mean Ki, 18 ± 5 μM) and is mixed (Kp >Km, Vmax >Vp) with respect to glucose 6-phosphate (mean crossover point, 0.5 ± 0.1 mM). The apparent Km(glucose 6-phosphate) is 0.37 ± 0.01 mM. The purified enzyme is inactivated in the light in the presence of dilute stroma and washed thylakoids, and by dithiothreitol. Enzyme which has been partially inactivated by treatment with dithiothreitol can be further inactivated in the light in the presence of dilute stroma and washed thylakoids and reactivated in the dark, but only to the extent of the reverse of light inactivation. Dithiothreitol-inactivated enzyme is not reactivated further by addition of crude stroma or oxidized thioredoxin. Dithiothreitol-dependent inactivation of the enzyme follows pseudo-first-order kinetics and shows rate saturation. The enzyme which has been partially inactivated by treatment with dithiothreitol does not differ from the untreated control with respect to thermal and tryptic inactivation. However, enzyme which has been partially light inactivated shows different thermal and tryptic inactivation patterns as compared to the dark control. These observations suggest that the changes in the enzyme brought about by light modulation are not necessarily identical with those brought about by dithiothreitol inactivation. 相似文献
35.
The hypothesis that chloroplasts having different light-saturated rates of photosynthesis will have different proportions of the intrinsic thylakoid complexes engaged in light-harvesting and electron transport (Anderson, J.M. (1982) Mol. Cell. Biochem. 46, 161–172) has been tested. Peas were grown in light regimes which varied in light intensity, quality and time of irradiance, and ranged from sunlight through red to blue-enriched light of very low radiation. The electron-transport capacity at saturating light of Photosystem I and Photosystem II of chloroplasts isolated from light-adapted peas was 2-fold and 5–6-fold lower, respectively, in the lowest radiation compared to sunlight. There was a marked increase in the amount of total chlorophyll associated with the main chlorophyll (LHCP1, LHCP2 and LHCP3) and a 2-fold decrease in the core reaction centre complex of Photosystem II (CP a) as the radiation decreased; the a ratio changed from 3.5 to 9.0. The amount of chlorophyll associated with Photosystem I varied from 34% in sunlight to 27% in the lowest radiation, but the antenna size of Photosystem I was not markedly different; there was a 2-fold decrease in the amount of cytochrome f on a chlorophyll basis, which partly accounted for the decreased electron-transport capacity of Photosystem I. Since the increases or decreases in the levels of each of the components correlated with decreasing radiation, it is clear that the light-adaptation of both light-harvesting and electron-transport components is indeed closely co-ordinated. 相似文献
36.
Redox titration of the electrochromic carotenoid band shift, detected at 50 μs after a saturating actinic flash, in spinach chloroplasts, shows that only one electron acceptor in Photosystem II participates in a transmembrane primary electron transfer. This species, the primary quinone acceptor, Q, shows only one midpoint potential (Em,7.5) of approx. 0 V and is undoubtedly equivalent to the fluorescence quencher, QH. A second titration wave is observed at low potential () and at greater than 3 ms after a saturating actinic flash. This wave has an action spectrum different from that of Photosystem II centers containing Q and could arise from a secondary but not primary electron transfer. A low-potential fluorescence quencher is observed in chloroplasts which largely disappears in a single saturating flash at ? 185 mV and which does not participate in a transmembrane electron transfer. This low-potential quencher (probably equivalent to fluorescence quencher, QL) and Q are altogether different species. Redox titration of C550 shows that if electron acceptor Qβ is indeed characterized by an Em,7 of + 120 mV, then this acceptor does not give rise to a C550 signal upon reduction and does not participate in a transmembrane electron transfer. This titration also shows that C550 is not associated with QL. 相似文献
37.
Bonnie J. Reger Maurice S.B. Ku Jeffrey W. Pottert John J. Evans 《Phytochemistry》1983,22(5):1127-1132
The ribulose-1,5-bisphosphate carboxylase/oxygenase purified from maize (a C4 monocot) to homogeneity has a MW of532 000 and sedimentation coeffici 相似文献
38.
Z. Krupa 《Photosynthesis research》1983,4(3):229-239
Thylakoid membranes obtained from bean chloroplasts treated with bean galactolipase or phospholipase A2 (from Crotalus terr. terr.) showed marked changes in their polypeptide patterns when separated on SDS-PAGE. The obtained results have been discussed with regard to the relationship between chloroplast lipids and polypeptides originating from chlorophyll-protein complexes of bean thylakoids. A coexistence between galactolipids and the peripheral antennae in PS I complex and LHCP3 as well as a conspicuous role of phospholipids in PSI and PSII centre chlorophyll-protein complexes has to be underlined.Abbreviations CP1
chlorophyll a-protein complex of PSI
- CPa
chlorophyll a-protein complex of PSII
- D10
digitonin subchloroplast particles enriched in PSII
- D144
digitonin subchloroplast particles enriched in PSI
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- LHCP1–3
light harvesting chlorophyll a/b protein complexes
- PAGE
polyacrylamide gel electrophoresis
- PSI
photosystem I
- PSII
photosystem II
- SDS
sodium dodecyl sulphate
- TCA
trichloroacetic acid
- Tricine
N-Tris-(hydroxymethyl)-methylglycine
- Tris
Tris-(hydroxymethyl)-aminomethan 相似文献
39.
Dose-response comparisons of canine plasma gastroenteropancreatic hormone responses to bombesin and the porcine gastrin-releasing peptide (GRP) 总被引:4,自引:0,他引:4
T J McDonald M A Ghatei S R Bloom T E Adrian T Mochizuki C Yanaihara N Yanaihara 《Regulatory peptides》1983,5(2):125-137
This study compares the potencies of the porcine gastrin-releasing peptide (pGRP) and bombesin, in causing elevations of canine plasma gastroenteropancreatic (GEP) levels. In the dose range 0-600 pmol . kg-1 . h-1, infusion of both peptides resulted in obvious dose-related elevations of plasma levels of gastrin, pancreatic polypeptide, enteroglucagon, immunoreactive pancreatic glucagon, and insulin. In this dose range, no significant difference in potency between the two peptides in elevating plasma levels of the above hormones was observed. The results of this study, demonstrating equimolar potency of pGRP and bombesin, are in contrast to previous studies reporting that pGRP was less potent than bombesin in causing certain bioactivities in the rat following intracranial administration of the two peptides. 相似文献
40.
Direct and indirect evidence for polypeptide absorption by the teleost gastrointestinal tract 总被引:2,自引:0,他引:2
The ability of the gastrointestinal tract of chinook salmon, Oncorhynchus tshawytscha , to absorb polypeptides in vivo was investigated by reference to the appearance of orally administered adrenocorticotropic hormone (ACTH) within the blood of fish previously treated with dexamethasone (3μg g−l body weight) in order to suppress endogenous ACTH secretion. Further, since cortisol presence within plasma is dependent upon the availability of ACTH, dexamethasone blockade of endogenous ACTH secretion, in conjunction with subsequent measurements of plasma cortisol levels, provides a means by which biological patency of absorbed exogenous ACTH may be demonstrated. Levels of ACTH and cortisol in plasma of dexamethasone-treated salmon were therefore measured for a period of 360 min immediately following oral intubation of ACTH (15μg g−1 body weight). Peak plasma presence of ACTH-like immunoreactivity (676.6 ± 33.6 pg ml−1 plasma) and cortisol (227.1 ± 29.0 ng ml−1 plasma) were recorded 120 min after ACTH administration. Results from the experimental groups were compared to those of 15 control treatments. Since administration of ACTH to chinook salmon elicited a consistent and significant elevation in not only plasma ACTH but also cortisol presence, it is contended that the salmonid gut expresses an ability to absorb polypeptides of dietary origin. The significance of these findings with respect to the oral administration of biologically active peptides and proteins to fish of importance to aquaculture is discussed. 相似文献