The competitive effect of adenosine-5'-triphosphate against the stimulating and inhibiting actions of 2,4-dinitrophenol on the mitochondrial respiration

Effect of ATP and substrates on 2,4-dinitrophenol-induced adenosine triphcsphatase (E. C. 3.6. 1. 4.) activity and respiration of isolated rat liver mitochondria has been investigated. 1. The oxidation of sodium succinate inhibited the action of 2, 4-DNP on the induction of adenosine triphosphatase activity in the mitochondria. 2. A moderately large amount of sodium succinate restored the suppressed mitochondrial respiration due to 2, 4-DNP. 3. Adenosine-5'-triphosphate (ATP) restored quantitatively the released and inhibited mitochondrial respiration due to 2,4-DNP, and its prior addition prevented also quantitatively the action of 2,4-DNP on the mitochondrial oxygen up-take. These ATP effects were oligomycin sensitive, and they were considered to manifest their actions through the phosphorylation system.</p

An isoform of the neuronal cyclin-dependent kinase 5 (Cdk5) activator

Neuronal Cdc2-like kinase is a heterodimer of Cdk5 and a 25-kDa subunit that is derived from a 35-kDa brain- and neuron-specific protein called the neuronal Cdk5 activator (p35/p25(nck5a)) (Lew, J., Huang, Q.-Q., Qi, Z., Winkfein, R. J., Aebersold, R., Hunt, T., and Wang, J. H. (1994) Nature 371, 423-426; Tsai, L. H., Delalle, I., Caviness, V. S., Jr., Chae, T., and Harlow, E. (1994) Nature 371, 419-423). Upon screening of a human hippocampus library with a bovine Nck5a cDNA, we uncovered a distinct clone encoding a 39-kDa isoform of Nck5a. The isoform, designated the neuronal Cdk5 activator isoform (p39(nck5ai)), showed a high degree of sequence similarity to p35(nck5a) with 57% amino acid identity. Northern blot analysis detected its mRNA transcript in bovine and rat cerebrum and cerebellum, but not in any other rat tissues examined. In situ hybridization showed that Nck5ai was enriched in CA1 to CA3 of the hippocampus, but absent in the fimbria of hippocampal formation. Among seven cell lines in proliferating cultures, only PC12 and N2A, two cell lines capable of differentiating into neuron-like cells, were found to contain Nck5ai mRNA. A 30-kDa truncated form of Nck5ai expressed as a glutathione S-transferase fusion protein in Escherichia coli] was found to associate with Cdk5 to form an active Cdk5 kinase. Thus, the isoform shares many common characteristics with p35(nck5a), including Ckd5 activating activity and brain- and neuron-specific expression. Both proteins show limited sequence homology to cyclins, suggesting that they define a new family of cyclin-dependent kinase-activating proteins

Changes in the expression of novel Cdk5 activator messenger RNA (p39(nck5ai) mRNA) during rat brain development

We previously reported that a neuron-specific Cdk5 activator, p35(nck5a), was most prominent in the newborn rat brain. In the adult brain, the expression decreased in most regions except hippocampus and primary olfactory cortex. A novel neuron-specific Cdk5 activator, p39(nck5ai), has been recently cloned. To clarify whether two activators were differentially distributed throughout brain development, in this study, we examined the spatial and temporal expression of p39(nck5ai) in the development rat brain. Northern blot analysis showed that p39(nck5ai) expression was low in 15-day old fetuses and newborn, and was most prominent in the 1-3 week-old rat brains. In the adult rat brain, expression declined to the same level as in newborn rat brain. In situ hybridization showed that p39(nck5ai) mRNA was weakly expressed in all neurons of all regions in the newborn rat brain and the transcriptional level was highest in all regions in the 3 week-old rat brain. In the adult, expression was decreased in most neurons except Purkinje and granule cells in the cerebellum which retained high levels. These results suggest that p35(nck5a) and p39(nck5ai) may have different functional roles in distinct brain regions during different states of the rat brain development. (C) 1997 Elsevier Science Ireland Ltd

Developmental alteration of the expression and kinase activity of cyclin-dependent kinase 5 (Cdk5)/p35(nck5a) in the rat retina

Neuronal Cdc2-like kinase has been purified from the bovine brain as a proline-directed serine/threonine kinase. This kinase is a heterodimer of Cdk5 and p35(nck5a) and influences neuronal maturation or sprouting in the normal brain. In this study, we showed the expression of Cdk5/p35(nck5a) kinase in the developing rat retina. The expression of Cdk5 and p35(nck5a) increased between 1 week and 3 weeks after birth. These expression levels were most prominent from 2 weeks to 3 weeks after birth and decreased after 4 weeks. The developmental change of Cdk5/p35(nck5a) kinase activity coincided with those of the expression of p35(nck5a) and Cdk5. An immunohistochemical study showed that Cdk5 was expressed in the ganglion cells and in some cells in the inner nuclear layer at an early stage. With retinal development, Cdk5 was expressed in the inner plexiform layer also. In the adult, the expression of Cdk5 was restricted to the inner plexiform layer and to some cells in the inner nuclear layer. These changes of localization in the developing retina were very close to those of B-50/GAP-43. On the other hand, the expression of p35(nck5a) was restricted to the soma of the neuron in the developing retina. This subcellular localization in the developing retina agreed with that in the developing rat brain. The expression levels of Cdk5 and p35(nck5a) in retina of rats raised from fetus to 3 weeks after birth in darkness were 36\% and 40\% respectively, of the baseline for control rats. Moreover, the kinase activity in rats raised in darkness was lower than that in control rats. These data suggest that Cdk5/p35(nck5a) may play a role in neuronal plasticity in the developing rat retina

Population Decline of Loggerhead Turtles: Two Potential Scenarios for Fethiye Beach, Turkey

Based on nesting data over a 12-year period (1993-2004), this study points to a negative population trend of the loggerhead turtle population at Fethiye beach, Turkey. The number of nests fluctuated from a maximum of 186 in 1995 to a minimum of 58 in 2004. Successively smaller peaks at 3-year intervals were followed by successively smaller troughs. Two analyses-one representing a dampened oscillation, the other retaining the period and the amplitudes of the nesting cycles-predict that nest number will drop to about 40-50 by 2015, i.e. to about 22-27% of its highest value. This drop at Fethiye does not correspond with a visible increase at neighboring beaches, leading to the interpretation that the number of nesting turtles here is declining. Moreover, the carapace size of emerging adult females is apparently decreasing, as are clutch sizes. Such a potential negative trend at a key Turkish nesting beach is cause for concern, an incentive for continued study, and a call for more coordinated and effective conservation programs in this region of the Mediterranean