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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The extent of the deactivation of the mitochondrial succinate dehydrogenase by oxaloacetate is a function of the redox state of the enzyme. Oxidized enzyme is deactivated by much lower concentrations of oxaloacetate than those needed to deactivate reduced enzyme. An accurate method for measuring this relationship is the redox titration of the enzymic activity of succinate dehydrogenase, carried out in the presence of oxaloacetate. For each concentration of oxaloacetate a different redox titration curve was reported with the apparent mid-potential decreasing with increasing oxaloacetate. These results are compatible with a model which proposes that both oxidized and reduced enzymes can form the catalytically non-active complex with oxaloacetate, but that the complex formed the the oxidized enzyme is more stable than that formed by the reduced enzyme. When the oxaloacetate concentration is low, reduction of the enzyme will lower the fraction of the succinate dehydrogenase-oxaloacetate complex, a reaction which we observe as reductive activation of the enzyme. If this experiment is repeated in the presence of high concentration of oxaloacetate, no activation of the enzyme takes place, but the low stability of the reduced enzyme oxaloacetate complex is revealed by the rapid exchange of the enzyme-bound oxaloacetate with the free ligand. The rate of this exchange is extremely slow at high positive potential and becomes faster upon lowering of the poise potential. The reductive activation of the succinate dehydrogenase is regarded as a two step reaction. In the first step the reduced non-active complex releases the oxaloacetate and in the second step the active form of the enzyme is evolved. These two steps can be observed experimentally; Reductive activation at a redox potential higher than the mid-potential of the oxaloacetate-malate couple (minus 166 mV) is characterized by Ea = 18 Kca/mole, the final equilibrium level of activation decreases upon lowering of the temperature. Reduction activation of the enzyme at minus 240 mV is a very rapid reaction which goes to completion at all temperatures tested and has an activation energy of 12.5 Kcal/mole. The mechanism of the reductive activation and its possible role in the regulation of succinate dehydrogenase in the mitochondria is discussed.
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PMID:The steady state activity of succinate dehydrogenase in the presence of opposing effectors.II. Reductive activation of succinate dehydrogenase in presence of oxaloacetate. 23 34

The hormone melatonin is synthesised and secreted from the pineal gland in darkness and triggers the daily and seasonal timing of various physiological and behavioural processes. The Mashona mole-rat, Cryptomys darlingi, lives in subterranean burrows that are completely sealed and is therefore rarely, if ever, exposed to light under natural conditions. Hence, this species is of particular interest for studies on rhythms of melatonin secretion. We investigated how plasma melatonin concentrations of the Mashona mole-rat responded to exposure to a long-term standard photoperiod of 12 h light, 12 h dark (12:12 LD), constant light (LL) and constant dark (DD). In addition, we examined whether plasma melatonin concentration was coupled to locomotor activity. Mashona mole-rats displayed rhythms of plasma melatonin concentration that appeared entrained to the standard LD photoperiod, suggesting that the mole-rat is capable of perceiving and entraining to this photic zeitgeber. Furthermore, under chronic constant lighting conditions (DD, LL), circadian rhythms in plasma melatonin concentration were observed, suggesting the possible existence of an endogenous rhythm. Light suppressed melatonin secretion, but constant light did not abolish the rhythm of plasma melatonin concentration. Between active and non-active animals, no difference in plasma melatonin concentration was found for any of the sequential photoperiods (LD1 DD, LD2, LL), tentatively suggesting that the rhythm of melatonin secretion is uncoupled from that of locomotor activity.
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PMID:Melatonin secretion in the Mashona mole-rat, Cryptomys darlingi--influence of light on rhythmicity. 1563 53

The social environment of animals can have profound implications on their behaviour and physiology. Naked mole-rats (Heterocephalus glaber) are highly social with complex dominance hierarchies that influence both stress- and reproduction-related hormones. Homeostasis may be affected by aggressive interactions, colony instability and social isolation. Furthermore, naked mole-rat colonies are characterised by a marked reproductive skew; a single female and few males are reproductively active while other colony members are reproductively suppressed. Thus, there are distinct differences in related hormone concentrations between reproductively active and non-active animals; however, this changes when non-reproductive individuals are removed from the colony. We investigated the effects of social isolation and colony disruption on plasma cortisol and progesterone concentrations in non-breeding naked mole-rats. During colony disruption, we found a significant increase in cortisol concentrations in females removed from the colony for social isolation (experimental) as well as in females that remained in the colony (control). Cortisol concentrations were reduced in both groups after experimental animals were paired up. No changes in cortisol concentrations were observed in control or experimental males after removal from the colony or pairing. This suggests that the females, but not the males, found colony disruption and social isolation stressful. Upon removal from the colony, both control and experimental females showed a small increase in progesterone, which returned to basal levels again in the control animals. Experimental females showed a dramatic spike in progesterone when they were paired with males, indicating reproductive activation. The sex difference in the stress responses may be due to the stronger reproductive suppression imposed on females, or the increased likelihood of dispersal for males. It is clear that the social environment reflects on the endocrine correlates of animals living in a colony, and that the colony structure may affect the sensitivity of the animals to changes in their environment.
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PMID:Effect of colony disruption and social isolation on naked mole-rat endocrine correlates. 3247 Apr 74