Production of poly-β-hydroxybutyrate by thermophilic cyanobacterium, Synechococcus sp. MA19, under phosphate-limited conditions

Synechococcus sp. MA19, grown autotrophically under phosphate-limited conditions at 50 °C, produced poly--hydroxybutyrate (PHB) when intracellular phosphate content was 0.043–0.076mmol per g of cellular components. In the culture for 260h using Ca₃(PO₄)₂ as a phosphate source, strain MA19 accumulated PHB at 55% (w/w) of the dry cells and the amount of PHB produced was 2.4gl^–1 which was almost twice that without Ca₃(PO₄)₂ addition.     

Excitability Changes of the Mauthner Cell during Collateral Inhibition

Excitability changes during collateral inhibition of the goldfish Mauthner cell (M cell) were measured directly by stimulating the cell with current pulses applied through an intracellular electrode. Excitability was suppressed during the extrinsic hyperpolarizing potential (EHP) as well as during the collateral IPSP. The inhibitory effect of the EHP was shown to be comparable in intensity to the effect of the IPSP. Excitability changes in the M cell during collateral IPSP depended on changes in the membrane conductance as well as in the membrane potential. Some simple equations are advanced which describe the excitability change during the IPSP in terms of changes in membrane potential and conductance. It was also found that invasion of antidromic impulses into the M cell was suppressed during the EHP, but not during the collateral IPSP. Conductance increase during the IPSP did not interfere with the invasion of antidromic impulses.     

Mechanism of phorbol myristate acetate-induced lymphotoxin production by a human T cell hybridoma

Various hydroxyl radical scavengers markedly inhibited phorbol myristate acetate (PMA)-induced lymphotoxin (LT) production by a human T cell hybridoma, AC5-8. Among those we tested, tetramethylurea (TMU) was the most potent scavenger, and it was revealed that TMU must be added before 2 h have elapsed after PMA addition in order for LT production to be inhibited. In concordance with this fact, soluble NADPH dependent O2- forming enzyme(s) were activated several fold by PMA. PMA also induced DNA strand breaks, a process markedly inhibited by TMU. As expected, ADP-ribosyl transferase (ADPRT), which is well known to require DNA strand breaks for its enzymatic activity, was activated by PMA treatment. In addition, specific inhibitors for ADPRT, namely 3-amino-benzamide and nicotinamide, inhibited PMA-induced LT production. Taken together, these three successive events, activation of soluble NADPH dependent O2- forming enzyme(s), DNA strand breaks and activation of ADPRT, may be required for PMA-induced LT production by AC5-8.     

Calpastatin, an endogenous calpain-inhibitor protein, regulates the cleavage of the Cdk5 activator p35 to p25

Cyclin-dependent kinase 5 (Cdk5) is a Ser/Thr kinase that is activated by binding to its regulatory subunit, p35. The calpain-mediated cleavage of p35 to p25 and the resulting aberrant activity and neurotoxicity of Cdk5 have been implicated in neurological disorders, such as Alzheimer's disease. To gain further insight into the molecular mechanisms underlying the pathological function of Cdk5, we investigated the role of the calpain inhibitor protein calpastatin (CAST), in controlling the aberrant production of p25. For this purpose, brain tissue from wild-type, CAST-over-expressing (transgenic), and CAST knockout mice were analyzed. Cleavage of p35 to p25 was increased in extracts from CAST knockout mice, compared with wild-type. Conversely, generation of p25 was not detected in brain lysates from CAST-over-expressing mice. CAST expression was 5-fold higher in mouse cerebellum than cerebral cortex. Accordingly, p25 production was lower in the cerebellum than the cerebral cortex. Furthermore, the Ca(2+) -dependent degradation of p35 by proteasome was evident when calpain was inhibited. Taken together, these results suggest that CAST is a crucial regulator of calpain activity, the production of p25, and, hence, the deregulation of Cdk5. Therefore, impairment of CAST expression and its associated mechanisms may contribute to the pathogenesis of neurodegenerative disorders.     

Ultrastructure of poplar cortical cells during the transition from growing to wintering stages and vice versa

Summary Electron microscopic studies revealed that major cytological changes in the cortical cells of poplar (Populus euramericana cv. gelrica) began to occur in early September in conjunction with the metabolic transition from the growing to the wintering stage. During this transition, the cells became temporarily rich in endoplasmic reticulum, polysomes and vesicles. As the conspicuous formation of organelles progressed, the large vacuoles became smaller and filled with osmiophilic materials. Undefined organelles (protein-lipid bodies) also increased in number. From late October until March, organelles involved in protein synthesis were sparsely distributed in the cells, indicating that the number of these organelles is probably linked to the seasonal cycle of protein synthesis. In early February, after release from dormancy, fusion of vacuoles proceeded in the cells. The inclusion of organelles and a gradual decrease in the amount of osmiophilic materials in the vacuoles occurred at this stage. Subsequently, the structure of the cells continued to undergo changes to accommodate growth, which occurred in early May.     

Adrenomedullin induces matrix metalloproteinase-2 activity in rat aortic adventitial fibroblasts

Background

The delicate balance of the extracellular matrix (ECM) determines the stiffness of the vascular wall, and adventitial fibroblasts are involved in ECM formation by synthesizing and degrading matrix proteins. In the present study, we examined the effect of the bioactive peptide adrenomedullin (AM) on activity and expression of matrix metalloproteinases (MMPs) in cultured aortic adventitial fibroblasts.

Methods and results

In cultured adventitial fibroblasts isolated from aorta of adult Wistar rats, 10⁻⁶ mol/L angiotensin II (Ang II) significantly (p < 0.05) down-regulated MMP-2 activity as determined by in vitro gelatin zymography. In contrast, 10⁻⁷ mol/L synthetic rat AM significantly (p < 0.05) stimulated zymographic MMP-2 activity by 23%, increasing intracellular cAMP, and AM abolished the action of Ang II, augmenting the MMP-2 activity. Similarly, Ang II down-regulated MMP-2 protein expression assessed by Western blotting, whereas AM increased it. Furthermore, 8-bromo-cAMP, an analogue of cAMP, mimicked the effect of AM, and H-89, an inhibitor for protein kinase A (PKA), significantly decreased the basal and AM-induced MMP-2 activity.

Conclusion

This study provides a new insight into the biological action of AM and its intracellular signaling system of cAMP/PKA stimulating the matrix degrading enzyme MMP-2, suggesting an important role for this molecule in modulating ECM deposition in the adventitial layer.     

Spinach chloroplasts scavenge hydrogen peroxide on illumination

Intact spinach chloroplasts isolated by the modified silicasol density centrifugation scavenged H₂O₂ on illumination ata rate about 3-fold that of bicarbonate-dependent O₂-evolution.Accompanying the disappearance of 1 mole of H₂O₂ is the evolutionof a half mole of O₂. The photoscavenging of H₂O₂ was inhibitedby 3(3,4-dichloro-phenyl)-l, l-dimethylurea, cyanide and azide.These results indicate that in chloroplasts H₂O₂ is reducedto H₂O by a cyanide and azide-sensitive peroxidase using a photoreductantas an electron donor. (Received July 4, 1980; )     

Blocking synaptic transmission with tetanus toxin light chain reveals modes of neurotransmission in the PDF-positive circadian clock neurons of Drosophila melanogaster

Circadian locomotor rhythms of Drosophila melanogaster are controlled by a neuronal circuit composed of approximately 150 clock neurons that are roughly classified into seven groups. In the circuit, a group of neurons expressing pigment-dispersing factor (PDF) play an important role in organizing the pacemaking system. Recent studies imply that unknown chemical neurotransmitter(s) (UNT) other than PDF is also expressed in the PDF-positive neurons. To explore its role in the circadian pacemaker, we examined the circadian locomotor rhythms of pdf-Gal4/UAS-TNT transgenic flies in which chemical synaptic transmission in PDF-positive neurons was blocked by expressed tetanus toxin light chain (TNT). In constant darkness (DD), the flies showed a free-running rhythm, which was similar to that of wild-type flies but significantly different from pdf null mutants. Under constant light conditions (LL), however, they often showed complex rhythms with a short period and a long period component. The UNT is thus likely involved in the synaptic transmission in the clock network and its release caused by LL leads to arrhythmicity. Immunocytochemistry revealed that LL induced phase separation in TIMELESS (TIM) cycling among some of the PDF-positive and PDF-negative clock neurons in the transgenic flies. These results suggest that both PDF and UNT play important roles in the Drosophila circadian clock, and activation of PDF pathway alone by LL leads to the complex locomotor rhythm through desynchronized oscillation among some of the clock neurons.