Electron Flow to the Intersystem Chain from Stromal Components and Cyclic Electron Flow in Maize Chloroplasts, as Detected in Intact Leaves by Monitoring Redox Change of P700 and Chlorophyll Fluorescence

The functional pool size of electrons in the intersystem chainof the chloroplasts of maize was estimated to be about 25 perP700 by the redox change in P700 with single- and multiple-turnoverlights under far-red light in intact leaves. This is about twicethe pool size observed in C₃ plants. Furthermore, the stromalpool size of electrons that can be donated to P700⁺ after actinicillumination was larger in maize leaves than in leaves of C₃plants, giving a maximum value of 225 electrons per P700. Maizeleaves showed an increase in the yield of modulated Chl fluorescenceafter turning off of actinic light, which confirms the donationof electrons in the dark to the intersystem chain from the stromaldonors that accumulated during actinic illumination. We proposethat the mesophyll chloroplasts are responsible for a high levelof electron-donating activity to the intersystem chain fromstromal donors such as triose phosphates and malate with NADPHas an intermediate. The level of P700⁺ under strong far-redlight was decreased after actinic illumination, suggesting theoperation of an actinic light-triggered cyclic electron flowin chloroplasts of the bundle sheath cells. (Received August 14, 1992; Accepted October 13, 1992)     

Mutation induced by drying of Escherichia coli on a hydrophobic filter membrane.

Drying of Escherichia coli to a required cellular water level was conducted on a hydrophobic membrane at the corresponding relative humidity. Mutation from an arginine auxotroph to the prototroph was induced by drying to a water activity (aw) of 0.53 and below, but not to an aw of 0.75 and above. The critical aw below which mutation occurred in the course of drying was similar to that for induction of deoxyribonucleic acid (DNA) strand breakage in the bacteria. Some ultraviolet or gamma-irradiation-sensitive strains, e.g., strains of carrying recA, recB, and uvrA recA were more sensitive to drying than the wild-type strains or strains carrying uvrA and polA. The DNA strand breakage of every strain was observed to be to a similar extent after drying to an aw of less than 0.53. The drying-resistant strains repaired the damaged DNA partially during postdrying incubation in a growth medium but not in phosphate buffer solution, while the drying-sensitive strains could not at all. Significant mutation on drying occurred in the wild-type strains, strains carrying uvrA and polA, but not in strains carrying recA. It is, therefore, concluded that the mutation is caused by errors in rec-dependent repair of the drying-induced breakage in DNA.     

Brain hydrogen sulfide is severely decreased in Alzheimer's disease

Although hydrogen sulfide (H2S) is generally thought of in terms of a poisonous gas, it is endogenously produced in the brain from cysteine by cystathionine beta-synthase (CBS). H2S functions as a neuromodulator as well as a smooth muscle relaxant. Here we show that the levels of H2S are severely decreased in the brains of Alzheimer's disease (AD) patients compared with the brains of the age matched normal individuals. In addition to H2S production CBS also catalyzes another metabolic pathway in which cystathionine is produced from the substrate homocysteine. Previous findings, which showed that S-adenosyl-l-methionine (SAM), a CBS activator, is much reduced in AD brain and that homocysteine accumulates in the serum of AD patients, were confirmed. These observations suggest that CBS activity is reduced in AD brains and the decrease in H2S may be involved in some aspects of the cognitive decline in AD.     

Continuous ATP Regeneration Using Immobilized Yeast Cells

Arthrobacter simplex was screened as an α-keto-δ-guanidinovalerate (ketoarginine) assimilating organism. A characteristic feature was its growth on ketoarginine as a carbon source; it began to grow after an extremely long lag. Its growth was stimulated by addition of 0.02% yeast extract to the medium.

The results indicated the transamination of arginine-α-ketoglutarate (α-KGA) and the hydrolyzing reaction of ketoarginine into α-keto-δ-aminovalerate and urea. Two intermediates, ketoarginine and α-keto-δ-aminovalerate, were isolated and identified by various procedures. Coupling of the two reactions was demonstrated in cell-free extracts of arginine-grown cells; ketoarginine formed from arginine by transamination with α-KGA was hydrolyzed directly to α-keto-δ-aminovalerate and urea. The metabolic routes of arginine in microorganisms were discussed.     

Ascorbate in thylakoid lumen as an endogenous electron donor to Photosystem II: Protection of thylakoids from photoinhibition and regeneration of ascorbate in stroma by dehydroascorbate reductase

Photoinhibition of the electron transport activity from tyrosine Z (Y_Z) in PS II to NADP⁺in Tris-treated thylakoids was suppressed by electron donation with either diphenylcarbazide or ascorbate (AsA) during the photoinhibition treatment. This suggests that AsA prevents donor side-induced photoinhibition in vivo as an endogenous donor. AsA in the lumen is photooxidized to monodehydroascorbate (MDA) in Tris-treated thylakoids, as detected by electron spin resonance spectrometry, but not in oxygenic thylakoids. Redox analysis of pyridine nucleotide in the presence of either MDA reductase or dehydroascorbate (DHA) reductase showed that the MDA photoproduced in the lumen is disproportionated to AsA and DHA, and the DHA leaking into the stroma is reduced to AsA by DHA reductase. No leakage of MDA through the thylakoid membrane was observed. Thus, the DHA-reducing enzyme system is indispensable in maintaining AsA concentrations in chloroplasts.     

Human T-cell hybridomas producing lymphokines. II. Enhancement of lymphotoxin secretion from human T-cell hybridomas by phorbol myristate acetate

Human lymphotoxin (LT)-producing T-cell hybridomas were constructed by fusing concanavalin A-activated human peripheral blood lymphocytes with emetine-actinomycin D-pretreated human acute lymphatic leukemia cells. LT secretion from these hybridomas was considerably enhanced by stimulation with phorbol-12-myristate-13-acetate (PMA) and concanavalin A or PMA alone. A study using cloned hybrid lines revealed that PMA/Con A acted directly on the LT-producing clones. Furthermore, PMA/Con A stimulated A-B9-24, one of the cloned hybridomas, and secreted fourfold larger amounts of LT under serum-free conditions than under serum-containing conditions. However, MIF/MAF and LT-producing cloned hybrid line E10-20 secreted rather decreased amounts of MIF/MAF when stimulated with PMA, while the LT secretion from the same hybridoma was enhanced with PMA.     

Rediscovery of Nebela ansata (Amoebozoa: Arcellinida) in eastern North America: biogeographical implications

Aim The question whether free‐living protists are generally cosmopolitan is currently a matter of debate. In this study we investigate the geographical distribution of a distinctive testate amoeba species, Nebela ansata, and use our data to assess the potential for highly restricted distribution patterns in some protist species. Location Global. Methods We analysed (1) 3400 testate amoeba publications from North America and other continents, (2) unpublished slides of the Penard Collection of the Natural History Museum, London, UK, and (3) 104 Sphagnum samples from eastern North America. Non‐metric multidimensional scaling (NMDS) was used to visualize the similarities in testate amoeba community composition among 1012 North American samples, including two communities that contained N. ansata. Results We rediscovered N. ansata at a site in New Jersey located close to its type locality, and in Nova Scotia. We also report the existence of an apparently unpublished museum specimen originally collected from New Jersey. Our extensive literature survey confirmed the presence of this species only in the temperate part of eastern North America. The NMDS revealed that communities with N. ansata were less similar to each other than to communities from other parts of North America, suggesting that favourable habitats for N. ansata occur in other Sphagnum‐dominated peatlands, a habitat type that has been extensively sampled in North America and elsewhere. Main conclusions These data provide an unusually convincing case of a free‐living microorganism with a very limited distribution range in the temperate part of eastern North America. The remarkably restricted distribution of N. ansata highlights the extent of our ignorance about the natural history of free‐living microorganisms, and raises questions about the lack of attention to microbial diversity in conservation biology.     

Pyrazolo pyrimidine-type inhibitors of SRC family tyrosine kinases promote ovarian steroid-induced differentiation of human endometrial stromal cells in vitro

Reversible protein tyrosine phosphorylation, coordinately controlled by protein tyrosine kinases and phosphatases, is a critical element in signal transduction pathways regulating a wide variety of biological processes, including cell growth, differentiation, and tumorigenesis. We have previously reported that c-Src belonging to the Src family tyrosine kinase (SFK) becomes dephosphorylated at tyrosine 530 (Y530) and thereby activated during progestin-induced differentiation of human endometrial stromal cells (i.e., decidualization). In this study, to elucidate the role of decidual c-Src activation, we examined whether 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1) and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), both potent and selective SFK inhibitors, affected the ovarian steroid-induced decidualization in vitro. Unexpectedly, PP1 paradoxically increased the kinase activity of decidual c-Src together with dephosphorylation of Y530 in the presence of ovarian steroids. Concomitantly, PP1 enhanced morphological and functional decidualization, as determined by induction of decidualization markers, such as insulin-like growth factor binding protein-1 and prolactin. PP2 also advanced decidualization along with up-regulation of the active form of c-Src whose Y-530 was dephosphorylated. In contrast to PP1 and PP2, herbimycin A, a tyrosine kinase inhibitor with less specificity for SFKs, showed little enhancing effect on the expression of both IGFBP-1 and active c-Src. These results suggest that SFKs, including c-Src, may play a significant role in stromal cell differentiation, providing a clue for a possible therapeutic strategy to modulate endometrial function by targeting signaling pathway(s) involving SFKs.     

Preterm birth without progesterone withdrawal in 15-hydroxyprostaglandin dehydrogenase hypomorphic mice

Parturition is a complex mammalian physiological process whose fundamental determinants have remained elusive. The increasing incidence of human preterm birth, a leading cause of infant mortality, highlights the importance of further understanding mechanisms regulating the timing of birth. Parturition is initiated in most nonprimate mammals, including mice, through a decrease in circulating progesterone caused by elevated prostaglandins. In humans, other higher primates, and guinea pigs, no consistent decrease in circulating progesterone occurs before the onset of labor. The divergence in endocrine control of labor initiation between most mammals compared with the great apes and guinea pigs gives rise to the question: how could a mechanism for the initiation of labor not requiring the withdrawal of progesterone evolve? Here, we genetically modulate prostaglandin signaling to determine the role of prostaglandin catabolism in the timing of birth. We find spontaneous preterm labor in the absence of progesterone withdrawal in 15-hydroxyprostaglandin dehydrogenase hypomorphic mice. The onset of labor in these hypomorphic mice is preceded by prematurely increased concentrations of prostaglandin E(2) and F(2alpha). Moreover, genetic crosses demonstrate a role for fetal genotype in birth timing. Together, these findings demonstrate a 15-hydroxyprostaglandin dehydrogenase-dependent shift in the physiology of murine parturition to one resembling the physiology of higher primates. Thus, endocrine control of labor has the capacity to plastically adapt to changes in genetically determined prostaglandin signals.