Ca2+ inhibition of adenyl cyclase of rabbit jejunal mucosa

Ca2+ ions at a concentration of 10-7--10-3 M inhibit adenylate cyclase of the rabbit jejunum mucosa (K0.5= =10-4 M). This effect is not modified after the membrane extraction by 10-3 M EDTA solution with a high or low ionic strength or after removal from the membrane preparation of Ca2+-dependent thermostable regulatory protein. The inhibition by Ca2+ions was discovered also in the presence of adenylate cyclase irreversible activators (guanylylimidodiphosphate and NaF), which points to the spontaneous interaction of Ca2+ ions with the catalytic subunit of the adenylate cyclase complex.     

Studies on the assay and activities of guanyl and adenyl cyclase of rat liver

In applying recently developed methods for measuring adenyl and guanyl cyclase activities, we found that some modifications produced much better cyclic nucleotide recovery, lower assay backgrounds, and greater reliability than previously reported. The reliability and specificity of the assay methods were confirmed by substrate and product analysis. Kinetic analysis of rat liver guanyl and adenyl cyclase was subsequently performed to investigate regulatory properties of both enzymes. The Michaelis-Menton constant of guanyl cyclase activity of a 30,000g supernatant fraction of rat liver for guanosine 5′-triphosphate (GTP) was 0.04 mm. This enzyme was competitively inhibited by adenosine 5′-triphosphate (ATP) (K_i = 0.011 mM). Guanyl cyclase was activated in vitro by secretin but unaffected by carbamylcholine, hist-amine, methoxamirie, serotonin, glucagon, and pancreozymin. Liver homogenate adenyl cyclase had a Michaelis-Menten constant for ATP of 0.2 mm. This enzyme was activated by secretin, pancreozymin, glucagon, sodium fluoride, and isoproterenol. GTP (0.005 mm) enhanced the activation by both isoproterenol and glucagon. Methoxamine had no effect on adenyl cyclase activity in the presence or absence of GTP. These results suggest that both guanyl cyclase and adenyl cyclase may be mediators of hormone action in the liver.     

Light-activated adenyl cyclase from Trichoderma viride

The effect of light on adenyl cyclase (E.C. 4.6.1.1) and 3':5'-cyclic-AMP-phosphodiesterase (E.C. 3.1.4.17) activity of Trichoderma viride was investigated. Adenyl cyclase proved to be a membrane-associated enzyme, requiring Mn2+ and was activated by light. In contrast, 3':5'-cyclic-AMP-phosphodiesterase showed no light-stimulated activity. The activity of 3':5'-cyclic-AMP-phosphodiesterase was present mainly in the cytosol and was stimulated by Mg2+.     

A note on supporting matrices for adenyl cyclase

Five insoluble matrices are described for the solid-support of solubilized cardiac adenyl cyclase. Straight forward chemistries are proposed for the reactions involved and for at least one matrix, an apparent purification of the cyclase activity was observed.     

HCl causes less intracellular acidification in Necturus gastric mucosa surface epithelial cells than other acids

Luminal acid causes intracellular acidification in the gastric epithelium, but the mechanism by which H(+) enters surface cells remains obscure. This study addressed the problem by assessing how different acids affect intracellular pH in gastric surface cells. Isolated Necturus maculosus antral mucosa was exposed to HCl, HNO(3), H(2)SO(4), and H(3)PO(4) at pH 2.30. Intracellular pH was measured with microelectrodes. The physicochemical interaction of a synthetic model of gastric phospholipids with the different acids was studied using Langmuir film balance. Exposure to luminal HNO(3), H(2)SO(4), or H(3)PO(4) caused significantly larger intracellular acidification than exposure to HCl. The degree of acidification was not dependent on the valence or nature of the anionic counterion of the acid but significantly correlated with the amount of molecular acid. By Langmuir film balance, subphases acidified with HNO(3), H(2)SO(4), or H(3)PO(4) caused more close packing of phospholipid molecules than those acidified with HCl, possibly allowing hydrogen bonding between head groups to facilitate H(+) movement across the phospholipid membrane. HCl causes significantly less intracellular acidification in gastric epithelium than HNO(3), H(2)SO(4), or H(3)PO(4). This may be caused by the lower amount of molecular HCl in solution and possible hydrogen bonding between the head groups of phospholipid molecules and the other acids.     

Tetrahydrocannabinol inhibits adenyl cyclase in human leukemia cells

Delta 9-tetrahydrocannabinol has been shown to induce incomplete maturation in ML2 human leukemia cell lines. We extend the observation of its induction of morphologic maturation to HL60 cells and of its induction of growth restriction to HL60 and K562 cells. We show that tetrahydrocannabinol reduces the cyclic AMP content of ML2 cells. Finally we demonstrate that this agent inhibits adenyl cyclase activity in ML2 cell membrane-enriched fractions. This finding in myeloid cells is compatible with one hypothesis of cannabinoid action in neuronal cells.