Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.25 (triphosphatase)
 1,529 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The properties of a cell surface nucleoside 5'-triphosphatase have been studied in small, intact, frog skeletal muscles, as a means of distinguishing the enzyme from other adenosine 5'-triphosphatases and of understanding its behaviour in the muscle membrane. The ectoenzyme in situ was shown to be a Ca2+- or Mg2+-activated ATPase liberating 7.5 +/- 0.4 (mean +/- SEM, n = 30) mumol of inorganic phosphate/g of muscle per 20 min, when the muscle was exposed to 2 mM ATP and 2 mM Ca2+ in Ringer's solution. The apparent Km for Mg2+ was 0.74 mM and for Ca2+ was 0.23 mM. A residual ATPase activity (20%) was found in the complete absence of divalent cations suggesting the existence of two ATPase types. A broad specificity toward nucleoside 5'-triphosphates was exhibited by the ecto-ATPase, but there was no nonspecific phosphatase activity. The enzyme was inhibited by La3+ and Cd2+, but was insensitive to ouabain, 2,4-dinitrophenol, oligomycin, and ruthenium red. Thus the ectoenzyme was not a Na+, K+-transport ATPase, was not an ATPase of mitochondrial origin, or a Ca2+-transport enzyme. Insulin had no effect. Inhibition by mersalyl, carbodiimide, and polar and cross-linking nonpolar nitrobenzene derivatives suggested that, for maximum activity, this membrane-bound enzyme required free sulfhydryl groups, certain free carboxyls, and an appreciable degree of hydrophobicity in its microenvironment.
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PMID:Characteristics of skeletal muscle ecto-ATPase in situ. 615 Jul 52

We have described a thyroid hormone receptor in synaptosomes of the chick embryo brain. To understand how the hormones exert their actions at this level, we performed a series of studies to demonstrate that this receptor could be linked to G proteins. Guanosine 5'-[gamma-thio]triphosphate (GTP gamma S)(100 muM) lowered the binding capacity of the receptor high affinity site from 8.9 +/- 1.3 to 3.4 +/- 1.3 ng T3/mg protein, a finding consistent with the coupling of receptor to G proteins. Furthermore, ADP ribosylation with pertussis toxin showed that thyroid hormones induced a dose-dependent increase in the inactive alpha 0-subunit of the G0 protein. This effect was detected at 10 pM, with a maximal increase (mean +/- SEM, 50 +/- 3.6%) at 100 nM, and T4 was as effective as T3. Both hormones also decreased the intrinsic guanine triphosphatase activity of G proteins by lowering the binding of GTP to the alpha-subunit and their rate of hydrolysis. This inhibition was greater with T4 (25 +/- 5%) than with T3 (14 +/- 2%), suggesting that the former could be the more active hormone at the synaptosomal level. The effect on guanine triphosphatase activity confirms that the synaptosomal thyroid hormone receptor is coupled to a G(zero) protein. These results demonstrate that thyroid hormones increase or favor the ADP ribosylation of G alpha(zero) by pertussis toxin. Thus, they enhance the alpha(zero)-GDP form of the G(zero) protein, namely its inactive conformation. By decreasing the activity of this protein, these hormones may modulate the formation of second messengers in synaptosomes and intervene in the regulation of neuronal proliferation and differentiation induced by several factors. Therefore, thyroid hormones may exert their action on brain maturation at least in part by modulating G alpha(zero) through their synaptosomal receptor.
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PMID:Effect of thyroid hormones on G proteins in synaptosomes of chick embryo. 864 Dec 9