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Biomedical subjects

F Murad

Publications and source records attributed to F Murad.

At least 235 records · Page 13Linked to original sources
PubMed1975

Activation of guanylate cyclase from rat liver and other tissues by sodium azide.

Sodium azide, hydroxylamine, and phenylhydrazine at concentrations of 1 mM increased the activity of soluble guanylate cyclase from rat liver 2- to 20-fold. The increased accumulation of guanosine 3':5'-monophosphate in reaction mixtures with sodium azide was not due to altered levels of substrate, GTP, or altered hydrolysis of guanosine 3':5'-monophosphate by cyclic nucleotide phosphodiesterase. The activation of guanylate cyclase was dependent upon NaN3 concentration and temperature; preincubation prevented the time lag of activation observed during incubation. The concentration of NaN3 that resulted in half-maximal activation was 0.04 mM. Sodium azide increased the apparent Km for GTP from 35 to 113 muM. With NaN3 activation the enzyme was less dependent upon the concentration of free Mn2+. Activation of enzyme by NaN3 was irreversible with dilution or dialysis of reaction mixtures. The slopes of Arrhenius plots were altered with sodium azide-activated enzyme, while gel filtration of the enzyme on Sepharose 4B was unaltered by NaN3 treatment. Triton X-100 increased the activity of the enzyme, and in the presence of Triton X-100 the activation by NaN3 was not observed. Trypsin treatment decreased both basal guanylate cyclase activity and the responsiveness to NaN3. Phospholipase A, phospholipase C, and neuraminidase increased basal activity but had little effect on the responsiveness to NaN3. Both soluble and particulate guanylate cyclase from liver and kidney were stimulated with NaN3. The particulate enzyme from cerebral cortex and cerebellum was also activated with NaN3, whereas the soluble enzyme from these tissues was not. Little or no effect of NaN3 was observed with preparations from lung, heart, and several other tissues. The lack of an effect with NaN3 on soluble GUANYLATE Cyclase from heart was probably due to the presence of an inhibitor of NaN3 activation in heart preparations. The effect of NaN3 was decreased or absent when soluble guanylate cyclase from liver was purified or stored at -20degrees. The activation of guanylate cyclase by NaN3 is complex and may be the result of the nucleophilic agent acting on the enzyme directly or what may be more likely on some other factor in liver preparations.

Animals↗
PubMed1975

Increased urinary excretion of cyclic guanosine monophosphate in rats bearing Morris hepatoma 3924A.

Urinary excretion of cyclic guanosine monophosphate (GMP) increased in rats bearing Morris hepatoma 3924A, and a correlation coefficient of .842 was observed comparing nucleotide excretion and tumor size. Irradiation of tumor or 5-fluorouracil administration delayed the increases in urinary cyclic GMP and tumor size. Surgical removal of tumors resulted in a rapid decline in cyclic GMP excretion to baseline levels. Cyclic adenosine monophosphate excretion was not altered by implantation, irradiation, or excision of tumor.

Animals↗
PubMed1975

Localization of particulate guanylate cyclase in plasma membranes and microsomes of rat liver.

The subcellular localization of guanylate cyclase was examined in rat liver. About 80% of the enzyme activity of homogenates was found in the soluble fraction. Particulate guanylate cyclase was localized in plasma membranes and microsomes. Crude nuclear and microsomal fractions were applied to discontinuous sucrose gradients, and the resulting fractions were examined for guanylate cyclase, various enzyme markers of cell components, and electron microscopy. Purified plasma membrane fractions obtained from either preparation had the highest specific activity of guanylate cyclase, 30 to 80 pmol/min/mg of protein, and the recovery and relative specific activity of guanylate cyclase paralleled that of 5'-nucleotidase and adenylate cyclase in these fractions. Significant amounts of guanylate cyclase, adenylate cyclase, 5'-nucleotidase, and glucose-6-phosphatase were recovered in purified preparation of microsomes. We cannot exclude the presence of guanylate cyclase in other cell components such as Golgi. The electron microscopic studies of fractions supported the biochemical studies with enzyme markers. Soluble guanylate cyclase had typical Michaelis-Menten kinetics with respect to GTP and had an apparent Km for GTP of 35 muM. Ca-2+ stimulated the soluble activity in the presence of low concentrations of Mn-2+. The properties of guanylate cyclase in plasma membranes and microsomes were similar except that Ca-2+ inhibited the activity associated with plasma membranes and had no effect on that of microsomes. Both particulate enzymes were allosteric in nature; double reciprocal plots of velocity versus GTP were not linear, and Hill coefficients for preparations of plasma membranes and microsomes were calculated to be 1.60 and 1.58, respectively. The soluble and particulate enzymes were inhibited by ATP, and inhibition of the soluble enzyme was slightly greater. While Mg-2+ was less effective than Mn-2+ as a sole cation, all enzyme fractions were markedly stimulated with Mg-2+ in the presence of a low concentration of Mn-2+. Triton X-100 increased the activity of particulate fractions about 3- to 10-fold and increased the soluble activity 50 to 100%.

Adenylyl Cyclases↗
PubMed1975

Two forms of guanylate cyclase in mammalian tissues and possible mechanisms for their regulation.

All mammalian tissues examined to date have two forms of guanylate cyclase with apparently different properties. From the studies in several laboratories, we suggest the following mechanisms for the possible regulation of guanylate cyclase activity: (1) factors that could alter the apparent cooperative nature of the enzyme, (2) interactions of metal ions with the substrate or enzyme, (3) factors that could overcome inhibition by ATP, (4) mechanisms that could regulate the interconversion of latent and active forms of the enzyme, (5) possible translocation of particulate and soluble forms of the enzyme, and (6) induction or repression of the enzyme.

Allosteric Regulation↗
PubMed1975

Increased particulate and decreased soluble guanylate cyclase activity in regenerating liver, fetal liver, and hepatoma.

We determined the activities of soluble and particulate guanylate cyclase [GTP pyrophosphatelyase (cyclizing); ?EC 4.6.1.2] IN REGENERATING RAT LIVER, FETAL AND NEONATAL RAT LIVER, AND HEPATOMA. TIn these tissues we found increased particulate and decreased soluble enzyme activities compared to normal adult rat liver. The particulate activity increased 12 hr after partial hepatectomy, reached maximal activity at 48 hr, and then declined. The soluble enzyme activity decreased within 8 hr and continued to decline. The activity of homogenates did not change. Guanylate cyclase activity was increased in plasma membrane and microsome fractions from regenerating liver. The increase in particulate activity was prevented with cycloheximide. Decreased soluble and increased particulate enzyme activities were found in fetal liver. After birth the soluble activity increased and the particulate activity decreased. Seven to 14 days after birth the activities of soluble and particulate fractions were similar to those of adult rat liver. In hepatoma 3924A, the activity of particulate guanylate cyclase was 9-fold greater and that of the soluble enzyme was 50% that of normal liver. These studies suggest that guanylate cyclase activity and its subcellular distribution may be related to liver growth through some unknown mechanism.

Animals↗
PubMed1975

Urinary excretion of adenosine 3',5'-monophosphate and guanosine 3',5'-monophosphate in normal children and those with cystic fibrosis.

The urinary excretion of adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP) was examined in 98 normal children and 46 children with cystic fibrosis between the ages of 9 months and 18 yr. Diurnal variations in cyclic AMP and cyclic GMP excretion were observed in subjects from either group, and peak levels of cyclic nucleotide excretion were generally observed during the period of 0700 to 2100 h. Excretion rates (mumol/day) of cyclic AMP and cyclic GMP increased significantly with age. When cyclic AMP and cyclic GMP excretion rates were normalized for urinary creatine, or body weight, the values declined significantly with age in both groups of patients. Cyclic GMP excretion normalized for body surface area also decreased with age, while the value for cyclic AMP (2.86 plus or minus 0.08 mumol/day/m2, mean plus or minus SE) was constant with age in both normals and cystic fibrosis children. With some comparisons of age groups there were significant differences in cyclic nucleotide excretion between normal subjects and children with cystic fibrosis. The differences noted were dependent upon the methods used to normalize excretion rates (urinary creatine, body weight, surface area, and the ratio of cyclic AMP to cyclic GMP excreated). In general patients with cystic fibrosis excreted greater amounts of cyclic GMP than did normals. The most striking comparison was the ratio of cyclic AMP to cyclic GMP excreted which was 9.09 plus or minus 0.50 in all normal children and 4.41 plus or minus 0.32 in children with cystic fibrosis (P smaller than 0.001).

Adolescent↗
PubMed1975

Requirement for a macromolecular factor for sodium azide activation of guanulate cyclase.

Sodium azide, a highly nucleophilic agent and a potent metabolic inhibitor, markedly increased guanylate cyclase activity from supernatant fractions of rat liver homogenates. The effect of sodium azide was not observed with partially purified guanulate cyclase from liver or crude soluble guanylate cyclase from cerebral cortex. However, the effect of sodium azide could be restored by the readdition of a fraction isolated from rat liver homogenates. The macromolecular factor required for the sodium azide effect was separated from soluble guanylate cyclase of rat liver with DEAE-cellulose column chromatography, and some of its properties were examined. The factor was nondialyzable and heat labile.

Animals↗