Cyclic nucleotides, thioldisulfide status of proteins, and cellular control processes

Exogenous Melatonin Enhances Moisture Stress Tolerance in Mango (Mangifera indica L.) through Alleviating Oxidative Damages

In subtropical regions, April to June represents a temporary moisture stress for mango trees, leading to huge economic loss. Although water is available in the deep root zone, the upper soil surface, which has fibrous roots, is dry, and the tree transpiration rate is high. Moisture stress causes an increased oxidation state, which is detrimental to fruit growth and development. Finding substitutes for moisture stress management is important for sustainable mango production. To manage this moisture stress in mango, we tested if foliar application of 20, 50, 100 and 150 μM melatonin helped to maintain a reduced oxidation state in the cells. Applications were made at three phenological stages of fruit development (marble, egg and mature fruit stages) in 16-year-old trees and the same plants for each treatment were followed over three years. Melatonin application indeed improved the fruit yield of mango. Moisture stress decreased yield by 55.94% compared to irrigated trees but only by 7.5% in melatonin treatment. Also, more 'A' grade fruits were harvested in irrigated and melatonin-treated conditions than in non-irrigated and non-treated conditions. Indeed, the total chlorophyll content in the leaves of moisture-stressed melatonin-treated trees (12.58 mg.g-1 fresh weight) was well above non-treated trees (6.77 mg.g-1) and similar to irrigated trees (12.50 mg.g-1). A dose-dependent increase in the chlorophyll content of melatonin-treated plants was found. Similarly, the activities of catalase, peroxidase, superoxidase dismutase enzymes in leaves of irrigated and melatonin-treated trees were lower than in non-irrigated condition, and superoxide free radial formation was lower in moisture-stressed melatonin-treated trees (0.77 nmol H2O2.mg-1 protein) and irrigated trees (0.65) than moisture-stressed non-treated trees (4.27). Significant variations was found in antioxidants (total, reduced and oxidized glutathione and ascorbate) content and antioxidant enzymes' activities (i.e., glutathione reductase and ascorbate peroxidase) in irrigated, melatonin-treated and non-irrigated conditions. Overall, 150 μM exogenous melatonin applied three times at different fruit development stages may be a sustainable and useful approach to manage transient moisture stress in mango trees thanks to its positive action on the antioxidant system.

Modulation of human gingival fibroblast cell metabolism by methyl mercaptan

Methyl mercaptan (CH3SH) is a malodorous compound whose levels are elevated in mouth and crevicular air of individuals with active periodontal disease. Since it may play a role in the disease process, its effects were evaluated using human gingival fibroblast cultures and viable porcine unkeratinized oral mucosal tissue sections. Results showed that the protein content of CH3SH-exposed cell cultures pulsed with [14C]-labelled glycine and proline was decreased by approximately 25%. Furthermore, this deleterious effect was irreversible in test cultures subsequently incubated for 24 h in a control 95% air/5% CO2 mercaptan-free environment. The supporting slab-gel electrophoresis profiles yielded evidence that exposure to CH3SH caused an alteration in collagen metabolism and a pooling of Type I procollagens. In addition, DNA synthesis was suppressed in CH3SH-exposed cultures by 44.1% at the 24 to 26 h peak of DNA synthesis. This is a true inhibition and not a shift in peak of maximum DNA synthesis as the shape and location of time-course curves of control and test systems is very similar. Proline transport study using [14C]-proline indicated a reduction in proline transport in the range of 40 to 50% in cultures exposed for 24 to 30 h to CH3SH. Significantly even 15 min exposure to 6.7 ng CH3SH/ml of incubating atmosphere suppressed proline transport by approximately 24%. This indicates that even brief exposure to low concentrations of CH3SH has a significant adverse effect on proline transport. Fluorescent staining of tissue sections exposed to mercaptan indicated that the agent elevated the number of cells stained with vital dye.(ABSTRACT TRUNCATED AT 250 WORDS)

Tubulin sulfhydryl groups as probes and targets for antimitotic and antimicrotubule agents

The sulfhydryl groups of tubulin are highly reactive entities. The reactivity of the sulfhydryl groups is sensitive to the presence of tubulin ligands, making these groups excellent probes for the interaction of tubulin with ligands. When tubulin is reacted with N,N'-ethylenebis-(iodoacetamide), two intrachain cross-links form in the beta subunit. Formation of one of these cross-links is completely blocked by colchicine, podophyllotoxin, and nocodazole; formation of the other is blocked completely by maytansine, phomopsin A and GTP and partly by Vinca alkaloids. Different ligands also differ in their effect on the rate of alkylation of tubulin with iodo[14C]acetamide, with vinblastine and phomopsin A being strong inhibitors and maytansine having very little effect. Oxidation of certain key sulfhydryl groups can inhibit microtubule assembly. One of these sulfhydryl groups appears to be cys239, but there are others not yet identified. Sulfhydryl-oxidizing agents also interfere with microtubule-mediated processes in vivo, raising the question of the existence of a physiological regulator of microtubule assembly. Potential physiological regulators have been examined to see if they can control microtubule assembly in vitro at their physiological concentrations. Of the ones that have been examined, thioredoxin and thioredoxin reductase are much better candidates for being physiological regulators than are either cystamine or glutathione.

The in vivo and in vitro oxidation of molecular form 1 of biliverdin reductase to molecular form 3 by diamide

Administration of phenylhydrazine to rats converted molecular form 1 of the liver biliverdin reductase into its disulfide bridged dimer (molecular form 3). This oxidative dimerization was shown not to be mediated by the NAD(+)-dependent dehydrogenase [(1984) Biochem. Biophys. Res. Commun. 121, 249-254]. Administration of diamide produced the same conversion. Although hepatic levels of GSH also decreased, no mixed disulfides of the reductase and GSH could be detected. Administration of the antioxidants allopurinol and alpha-tocopherol together with the diamide did not affect this conversion of molecular forms produced by the latter. The diamide also oxidized molecular form 1 of biliverdin reductase in vitro and molecular form 3 was formed. The chemical oxidation took place at a high rate and was partially inhibited by GSH but not by cysteine.

Sulfhydryl groups and peroxidase-like activity of albumin as scavenger of organic peroxides

The concentration, the reactivity of sulfhydryl (SH) groups and the peroxidase-like activity (PLA) of bovine serum albumin (BSA) have been determined in vitro after treatment with peroxides. Tert-butylhydroperoxide (tBOOH), cumene hydroperoxide (CuOOH), benzoyl hydroperoxide (BOOH) and hydrogen peroxide reacted with BSA, decreasing the titratable SH group concentration and increasing the value of the ratio between the reaction rate and the concentration of albumin SH groups in the sulfhydryl-disulfide exchange reaction. This value was defined as reaction constant (Kr). PLA of albumin was independent of the presence of the SH group, as SH depleted BSA maintained the same activity as the control. From our findings it derives that albumin may have two possibilities of scavenging peroxides: PLA and the SH group. The plasma SH concentration, Kr and PLA of albumin were also determined in carrageenan paw edema and in experimental adjuvant-arthritis in rats. A decrease in SH concentration, an increase in Kr and PLA of rat plasma albumin were observed in both inflammatory processes.

Mechanisms of membrane damage for CHO cells heated in suspension

Chinese hamster ovary cells were heated for 20 min at 45.5 degrees C in different conditions, and quantitative determinations of cellular membrane blebbing were performed for cells maintained at 25 degrees C and 37 degrees C after hyperthermia. The percentage of cells with blebs following heating was dependent upon the composition of the medium during heating and the posthyperthermia temperature after heating. The total extent of bleb formation after heating was independent of the calcium-ion concentration in the medium during heating; however, differences in the kinetics of bleb disappearance after heating point to the importance of Ca2+ concentration in the expression of heat damage. Without hyperthermia, blebs were formed on the cell-surface membrane with agents which block sulfhydryl groups or release calcium from cellular stores. The cells were protected from bleb formation when cells were incubated with glutathione before addition of sulfhydryl-blocking agents or heat treatment. Oligomycin did not prevent the formation of blebs, suggesting that this phenomenon is not energy-dependent. Only a small percentage of cells were covered with blebs when they were heated in saline solution. When cells were incubated with dbcAMP before heat, blebs did not appear at 25 degrees C. A possible interpretation for these observations is presented.

Dissociation of cells from sea urchin embryos alters the synthesis of actins and other proteins

The effects of altered cellular microenvironments on patterns of protein synthesis at various periods during sea urchin development were quantitated by comparing the relative incorporation of [35S]methionine into selected polypeptides of intact embryos and cells dissociated from them. The effects of increasing times of reassociation were also determined. Quantitative, but not qualitative, differences in incorporation were noted. Actins, as well as heterogeneous acidic polypeptides with an Mr of about 80 kDa, showed increased incorporation in dissociated cells labeled at the time control embryos were recently hatched blastulae. Labeling of another acidic group of polypeptides with an Mr of about 100 kDa was decreased. Possible mechanisms regulating these shifts in incorporation were investigated by the use of inhibitors. The dissociation-triggered changes were insensitive to actinomycin D, cordycepin, dibutyryl cAMP, 3-isobutyl-1-methylxanthine, and trifluoperazine; however, the latter two stimulated incorporation into some polypeptides in intact blastulae. Age-dependent shifts in incorporation were also detected in both intact embryos and dissociated/reassociating cells.

Assembly properties of fluorescein-labeled tubulin in vitro before and after fluorescence bleaching

Brain tubulin has been conjugated with dichlorotriazinyl-aminofluorescein (DTAF) to form a visualizable complex for the study of tubulin dynamics in living cells. By using several assays we confirm the finding of Keith et al. (Keith, C. H., J. R. Feramisco, and M. Shelanski, 1981, J. Cell Biol., 88:234-240) that DTAF-tubulin polymerizes like control tubulin in vitro. The fluorescein moiety of the complex is readily bleached by the 488-nm line from an argon ion laser. When irradiations are performed over short times (less than 1 s) and in the presence of 2 mM glutathione, a mixture of DTAF-tubulin and control protein (as occurs after microinjection of the fluorescent conjugate into living cells) will retain full polymerization activity. Slow bleaching (approximately 5 min) or bleaching without glutathione promotes formation of covalent cross-links between neighboring polypeptides and kills the polymerization activity of DTAF-tubulin, including some molecules that are neither cross-linked nor bleached. Even under conditions that damage DTAF-tubulin, however, DTAF-microtubules are not destroyed by bleaching. They will continue to elongate by addition of DTAF-tubulin subunits to their free ends, and they neither bind nor exchange subunits along their lateral surfaces. These results suggest that DTAF-tubulin is a suitable analog for tubulin, both in studies of protein incorporation and for investigations of fluorescence redistribution after photobleaching.

Ca2+, Mg2+ and (adenosine diphosphate ribose)n in cellular response to irradiation

A model of cellular response to irradiation involving adenosine diphosphate ribosylation (ADP-ribosylation) is proposed. Its main assumptions are (a) control of accessibility of sites for ADP-ribosylation in chromatin by free Ca2+/Mg2+ ratio; and (b) regulation of the Ca2+/Mg2+ ratio by factors affecting intracellular free Ca2+ concentration; the regulation would be mediated by mitochondria. The model seeks to explain the mechanism of action of radiomodifiers such as caffeine, local anaesthetics, polyamines and 2,4-dinitrophenol.

Studies on glutathione metabolism in ventral prostate and chemically induced prostatic carcinoma in rats

Glutathione content and the activity of glutathione reductase were examined in ventral prostate and chemically induced 11095 squamous-cell prostatic carcinoma in rats. Castration produced a significant reduction in the levels of reduced (GSH) and oxidized (GSSG) glutathione and glutathione reductase activity in the prostate. Replacement of testosterone (50 mg/kg) daily for 7 days to castrated animals elevated the reduced glutathione level and the activity of glutathione reductase almost to normal limits. Squamous-cell carcinoma was implanted in castrated and intact animals. Tumor growth in normal rats produced a decrease of almost 30% in the weight of the ventral prostate at 21 days post-implantation, although the glutathione levels remained unaffected. Much greater activity of glutathione reductase was detected in the tumor in comparison to the values noted for the normal tissue. The tumor also showed significantly higher values for the GSH/GSSG ratio. No apparent difference could be found in the rate of the growth of tumors whether implanted in normal or castrated animals. The levels of reduced and oxidized glutathione and glutathione reductase activity also seemed identical in tumors obtained from both groups of animals. Administration of testosterone (50 mg/kg) or beta-estradiol (2 mg/kg) daily for 11 days to tumor-bearing castrated animals did not alter the levels of glutathione and glutathione reductase activity. A significantly higher level of blood reduced glutathione was found in tumor-bearing rats in comparison to that seen for the normal subjects. Our results demonstrate that androgen depletion and replacement therapy influence the metabolism of glutathione in rat ventral prostate. Squamous-cell carcinoma of the prostate appears to differ from the normal tissue with respect to the observed androgen effects. There is dissimilarity in the metabolism of glutathione in the two tissues since greater activity of glutathione reductase and lower values of reduced glutathione were seen in the tumor as compared to those of the ventral prostate. Treatment with beta-estradiol, an antiprostatic agent, does not seem to influence the growth or glutathione metabolism of squamous-cell carcinoma of the prostate. The observed changes in blood glutathione levels might prove to be useful as an index of rapid growth of the neoplastic tissue.

Cell membrane receptor classes delimited through cap formation either with diamide or with membrane mobility agent, A2C

Receptors on normal human peripheral blood lymphocytes can be divided into two classes by means of the capping response exhibited in the presence of the reagents, diamide or colchicine (microtubule-related) and A2C (microtubule-independent). Diamide and colchicine promote capping of concanavalin A (Con A) receptors. Diamide capping is reversible, while colchicine capping is not reversible under the conditions used. A2C does not promote the capping of Con A receptors. In contrast, diamide and colchicine do not affect the rate at which either anti-immunoglobulin (anti-Ig) or wheat germ agglutinin (WGA) receptors cap, but A2C effectively enhances cap formation for both anti-Ig and WGA receptors. The simplicity of the classification method promises to be of use in the investigation of membrane receptors.

Increased cyclic AMP content directly correlated with morphological transformation of cells infected with a temperature-sensitive mutant of mouse sarcoma virus

Normal rat kidney cells infected with a cold-sensitive mutant of mouse sarcoma virus [NRK(MSV-lb)] morphologically transform when exposed to adenosine 3':5' cyclic monophosphate (cAMP) at the restrictive temperature. The cAMP-induced morphological changes occur rapidly and are reversible. Agents capable of elevating endogenous levels of cAMP [prostaglandin E1 (PGE1) and cholera toxin (CT)] induced morphological transformation of NRK(MSV-lb) cells at the restrictive temperature that was concentration dependent, potentiated by cAMP phosphodiesterase inhibitors, and not prevented by inhibitors of DNA, RNA, and protein synthesis. Prostaglandin E1 stimulated a transient increase in the intracellular level of cAMP with a concomitant morphological transformation and reversion of cells as cAMP levels decline. The maximum increase is reached by 10 min, followed by a decline to near basal level by 80 min. In contrast, incubation of cells with CT resulted in irreversible morphological transformation and increased levels of cAMP first detectable by 1 hr with maximum levels reached by 24 hr. Heated CT (100 degrees C, 20 min) was without effect. Addition of CT to reverted PGE1-treated cells resulted in morphological transformation suggesting the existence of discrete receptors in NRK(MSV-lb) cells.

New models of cellular control: membrane cytoskeletons, membrane curvature potential, and possible interactions

The concepts of "membrane cytoskeletons" (proteins attached to the cytoplasmic face of the membrane to give rigidity and control of lateral protein diffusion) and of membrane curvature potential are briefly reviewed. Possible modes of attachment of the membrane cytoskeleton to the bilayer are discussed, and a detailed calculation of possible sources of membrane curvature potential in the red cell is made. The 2 control systems are then used to illustrate possible mechanisms for some cellular processes, such as vesicle formation and release, pseudopod formation, and red cell aging. It is concluded that combination of these concepts allows control mechanisms which appear to act at a distance, or have other unusual systems properties.

Involvement of glutathione in the inhibition of sea urchin egg mitosis by phenyl glyoxal

Cell division in fertilized sea urchin eggs was reversibly inhibited when the ketoaldehyde phenyl glyoxal (PG) at a concentration of 0.1 mM was added to eggs for ten minutes prior to the formation of the mitotic spindle. We investigated whether inhibition of mitosis was due to PG binding to the cell surface (as previously suggested by Stein and Berestecky, '74) or to some intracellular effect. When 14C-PG was added to eggs, label was readily taken up into the egg cytoplasm; very little label was associated with the egg surface. In the cytoplasm PG combined with equimolar amounts of reduced glutathione (GSH), decreasing the levels of cellular GSH to less than 15% of normal and accounting for at least 50% of the PG taken up by eggs. The concentrations of oxidized and protein-bound glutathione were unaffected by PG treatment. We showed that glyoxalase enzymes were present in sea urchin eggs and were capable of metabolizing the PG-GSH complex, thereby restoring GSH to normal levels after PG was removed from the sea water. Though some other effect of PG cannot be ruled out, the major fate of PG in eggs was to combine with GSH, and the transient decrease in GSH which resulted could lead to inhibition of mitosis. While other reports (Nath and Rebhun, '76; Oliver et al., '76) have shown that reagents which oxidize GSH disrupt microtubule-related events, our results showed that such inhibition could be caused by decreased GSH levels alone.

Microtubule dynamics and glutathione metabolism in phagocytizing human polymorphonuclear leukocytes

Glutathione oxidants such as tertiary butyl hydroperoxide were shown previously to prevent microtubule assembly and cause breakdown of preassembled cytoplasmic microtubules in human polymorphonuclear leukocytes. The objectives of the present study were to determine the temporal relationship between the attachment and ingestion of phagocytic particles and the assembly of microtubules, and simultaneously to quantify the levels of reduced glutathione and products of its oxidation as potential physiological regulators of assembly. Polymorphonuclear leukocytes from human peripheral blood were induced to phagocytize opsonized zymosan at 30 degrees C. Microtubule assembly was assessed in the electron microscope by direct counts of microtubules in thin sections through centrioles. Acid extracts were assayed for reduced glutathione (GSH) and oxidized glutathione (GSSG), by the sensitive enzymatic procedure of Tietze. Washed protein pellets were assayed for free sulfhydryl groups and for mixed protein disulfides with glutathione (protein-SSG) after borohydride splitting of the disulfide bond. Resting cells have few assembled microtubules. Phagocytosis induces a cycle of rapid assembly followed by disassembly. Assembly is initiated by particle contact and is maximal by 3 min of phagocytosis. Disassembly after 5-9 min of phagocytosis is preceded by a slow rise in GSSG and coincides with a rapid rise in protein-SSG. Protein-SSG also increases under conditions in which butyl hydroperoxide inhibits the assembly of microtubules that normally follows binding of concanavalin A to leukocyte cell surface receptors. No evidence for direct involvement of GSH in the induction of assembly was obtained. The formation of protein-SSG, however, emerges as a possible regulatory mechanism for the inhibition of microtubule assembly and induction of their disassembly.