Cyclase

About: Cyclase is a research topic. Over the lifetime, 10162 publications have been published within this topic receiving 388566 citations.

beta-Adrenergic receptors and catecholamine-sensitive adenylate cyclase in rat fat-cell membranes: influence of growth, cell size and aging.

Abstract: The influence of age and cell size on adipocyte β-adrenergic receptors was studied using the binding of (−)-[3H]dihydroalprenolol to crude adipocyte membranes from rats of different ages (1–30 months). Age and cell size failed to modify the kinetics, the reversibility and the stereospecificity of (−)-[3H]dihydroalprenolol binding. Scatchard plots of the binding data obtained with membranes from young, adult and senescent rats showed the existence of binding sites with high affinity for (−)-dihydroalprenolol and which have the characteristics of the β-adrenergic receptors. The dissociation constant Kd of these sites was not affected by age (15.1–20.5 nM), suggesting that the receptor properties do not change during aging or fat cell enlargement. In contrast, the apparent maximal number of β-receptors varied with age and cell size: during completion of maturation (1–8 months), it increased proportionally to the fat cell surface, reaching at maturity the value of 40800 receptors per cell. With senescence (12–30 months), on the contrary, although cell size remained constant over this period, the number of β-receptors markedly declined, falling to 7200 receptors per cell in membranes from 30-month-old rats. These modifications were accompanied by parallel variations in the sensitivity of adenylate cyclase to catecholamines, but not to fluoride, suggesting that the catecholamine receptors and the adenylate cyclase catalytic sites develop independently. In contrast, the lipolytic responsiveness of adipocytes to catecholamines started to decline already during completion of maturation, an effect which seems thus to result from an action of age on one or more of the lipolytic steps localized beyond the catecholamine receptor-adenylate cyclase system.

Calcium is an inhibitor of luteinizing hormone-sensitive adenylate cyclase in the luteal cell.

Abstract: Both prostaglandin F2α (PGF2α) and LHRH inhibit LH-stimulated cAMP accumulation and progesterone secretion in the intact luteal cell, but have no effect on LH-sensitive adenylate cyclase activity in isolated membranes. The present studies were conducted to assess the possibility that calcium (Ca2+) may mediate the inhibitory activity of PGF2α and LHRH in the rat luteal cell. Removal of extracellular Ca2+ significantly enhanced cAMP accumulation in response to LH by about 2-fold, but blunted LH-stimulated progesterone secretion. Incubation of luteal cells with A23187 caused a highly significant and dose-related decrease in LH-stimulated cAMP accumulation with a concentration for half-maximal inhibition (IC50) of about 1 μm. No effect of A23187 was seen on LH-sensitive adenylate cyclase activity, but the ionophore elicited significant inhibition of LH-stimulated intracellular cAMP accumulation in the presence of isobutyl-methylxanthine (MIX), a phosphodiesterase inhibitor. Inhibition by A23187 was Ca2+ depe...

Regulation of adenosine 3':5'-monophosphate content of human astrocytoma cells: desensitization to catecholamines and prostaglandins.

Abstract: Human astrocytoma cells (1321N1) exhibit adenylate cyclase activities coupled to independent receptors for catecholamines and prostaglandins of the E-series. Exposure of the cells to either norepinephrine or prostaglandin E1 (PGE1) results in an initial rapid accumulation of cyclic AMP but also results in a progressive loss of responsiveness of the cells to agonists. Initially, the desensitization is in large part agonist-specific. However, with continued exposure to high concentrations of norepinephrine, partial loss of responsiveness to PGE1 occurs, and vice versa. The mechanism underlying this phenomenon does not appear to involve inactivation of the effectors, formation of an inhibitory substance in the culture medium or an increase in the rate of excretion of cyclic AMP from the cell. Blockade of protein synthesis (85%) by 5 mug/ml cycloheximide did not change the rate or extent of desensitization. When desensitized cells were incubated in the presence of the effectors, responsiveness was essentially completely recovered with a t1/2 of 5-7 hr. Cycloheximide recovery reduced. Norepinephrine-induced desensitization to either norepinephrine or PGE1 was blocked by sotalol, a beta receptor blocking agent. Incubation of the cells with dibutyryl cyclic AMP caused desensitization to both norepinephrine and PGE). The results suggest that catecholamine-induced desensitization occurs as a result of interaction of the agonist with the same receptor that is linked to activation of adenylate cyclase. Cyclic AMP appears to mediate at least the non-specific aspect of agonist-induced desensitization.

Postsynaptic Serotonin-Sensitive Adenylate Cyclase in the Central Nervous System: I. Development and Distribution of Serotonin and Dopamine-Sensitive Adenylate Cyclases in Rat and Guinea Pig Brain

Abstract: Postsynaptic serotonin-sensitive adenylate cyclase with an apparent affinity of 1 µM for serotonin (5-HT) was detected in various structures of the central nervous system in the rat and the guinea pig. At birth, the regional distribution of this enzyme in the rat brain was closely correlated with the topographical distribution of the serotoninergic innervation in young (9-day-old) as well as adult animals. Electrolytic raphe lesions made on the fourth day after birth, which produced 90% degeneration of serotoninergic innervation in rat colliculi, did not alter the characteristics (apparent affinity and maximal activity) of the serotonin-sensitive adenylate cyclase in this area. This suggests that the serotonin-sensitive adenylate cyclase is associated with postsynaptic serotoninergic receptors in the brain. During development, in both the rat and the guinea pig, the amount of cyclic 39,59-AMP formed in response to an optimal concentration of serotonin in a given area remained constant. This is in contrast to the amount of cyclic AMP formed in response to an optimal concentration of dopamine, which increased 6-fold in the rat striatum between the second and 23rd days after birth. The lack of correlation between the regional distribution of the dopamine-sensitive adenylate cyclase and serotoninergic innervation and between the serotonin-sensitive adenylate cyclase and dopaminergic innervation further emphasizes that the serotonin- and dopamine-sensitive adenylate cyclases are each associated with specific receptors in the rat brain.