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M J Martinez

Publications and source records attributed to M J Martinez.

At least 37 records · Page 2Linked to original sources
PubMed1996

Role of adenine nucleotides in the activation of microsomal cholesterol ester hydrolase by fructose or adenosine in rat hepatocytes.

In the present study we have analysed the potential relationship between the cellular level of adenine nucleotides and the activity of microsomal cholesterol ester hydrolase by treating rat hepatocyte suspensions with fructose or adenosine. Fructose raised the microsomal hydrolysis of cholesteryl esters as a function of the dose. This ketose led to marked decreases in the cell level of ADP, ATP and total adenine nucleotide whereas that of AMP increased slightly, thus giving a rise in the cellular AMP/ATP ratio. The effects remained virtually constant over a period of 60 min. Incubation of hepatocytes in a Ca(2+)-free medium with or without ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid blocked by 40% the fructose-induced activation of cholesterol esterase whereas the rise in AMP/ATP was unaffected. Adenosine caused dose-dependent activations of cholesterol ester hydrolase and raised AMP, ADP and ATP concentrations as well as the AMP/ATP ratio. 2-Chloro-adenosine and N6-[L-2-phenyl-isopropyl] adenosine, non-metabolizable analogues of adenosine, did not mimic the effects of the nucleoside. A positive linear correlation exists between the percentage rises in the activity of microsomal cholesterol ester hydrolase and those in the intracellular AMP/ATP ratio in fructose- or adenosine-treated cells. These results indicate that, in microsomes from intact hepatocytes, the breakdown of cholesteryl esters to yield cholesterol and fatty acids is stimulated by fructose and adenosine and this can be explained in part by the increase in the cellular AMP/ATP ratio. In the case of fructose, also a Ca(2+)-dependent mechanism is involved.

AMP Deaminase↗
PubMed1996

Comparison of the effects of cyclic AMP analogues on cholesterol metabolism in cultured rat and hamster hepatocytes.

The effects of two cell-permeable cyclic AMP analogues, 8-chloro cyclic AMP (8-Cl cAMP) and 8-(4-chlorophenylthio) cyclic AMP (8-CPT cAMP), on cholesterol esterification, cholesteryl ester hydrolysis and bile acid synthesis were compared in cultured rat and hamster hepatocytes. Cholesterol esterification, as measured by the incorporation of [3H]oleate into cholesteryl ester, was increased by 58-88% by the analogues in rat hepatocytes and by 33-43% in hamster cells. The response in rat hepatocytes, however, was observed after a relatively short incubation time (28% increase after 1 hr), whereas that in hamster cells required a longer period (36% after 12 hr) to become apparent. The activity of the cytosolic neutral cholesteryl ester hydrolase in rat hepatocytes was also stimulated by both cyclic AMP analogues (31-37%, but the microsomal activity was unaffected. In hamster hepatocytes, however, microsomal cholesteryl ester hydrolase activity was increased (47-80%) in the presence of 8-Cl cAMP or 8-CPT cAMP. Bile acid synthesis was increased by 8-CPT cyclic AMP in rat cells (approximately 25%) but was unchanged by both analogues in hamster hepatocytes. These results indicate significant differences in the way in which cholesterol metabolism responds to cyclic AMP in cultured rat and hamster hepatocytes.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Manganese-Mediated Lignin Degradation by Pleurotus pulmonarius.

Pleurotus pulmonarius produced the strongest degradation of lignin during solid-state fermentation of [(sup14)C]lignin wheat straw with different fungi. A manganese-oxidizing peroxidase seemed to be involved in lignin attack, since the addition of Mn(sup2+) to the culture increased lignin mineralization by ca. 125%. This enzyme was purified and characterized from both solid-state fermentation and liquid cultures.

Journal Article↗
PubMed1995

Inhibition of microsomal cholesterol ester hydrolase by okadaic acid in isolated rat hepatocytes.

Okadaic acid, a potent and specific inhibitor of protein phosphatases 1 (IC50 10-20 nM) and 2A (IC50 0.05-2 nM) caused early and sustained inhibitions of microsomal cholesterol ester hydrolase activity in hepatocyte suspensions. The changes in the kinetic properties of the esterase and its response to exogenous alkaline phosphatase and cyclic AMP-dependent protein kinase after cell exposure to 1 microM or 1 nM okadaic acid differed markedly among themselves, which suggests the involvement of both protein phosphatases 1 and 2A in the regulation of the microsomal hydrolysis of cholesterol esters. Furthermore, the inhibitory effect of okadaic acid is likely to be independent of the dibutyryl-cyclic AMP promoted cell events leading to stimulation of esterase activity.

Animals↗
PubMed1995

Quantitative measurement of muscle strength in the mouse.

We have designed a special dynamometer for measuring mouse forelimb muscle strength and endurance. The device exploits a mouse's tendency to grasp a horizontal metal bar while suspended by its tail. A threshold value for the magnitude and duration of force that the mouse can exert is obtained by first allowing the animal to grasp the bar and then applying a steadily increasing downward force to the opposite end of a cable to which the mouse attaches. The bar is attached to a force transducer and pen recorder to produce a permanent record of the force produced by the mouse. Test results show that this dynamometer provides quantitative measurements of muscle strength and endurance in the mouse. Comparisons between experimental groups of normal and wobbler mice, a model for lower motor neuron disease, show that both the force exerted by the animals (muscle strength), and the duration of the pull (endurance), can be quantified and statistically analyzed. This technique can be used as an assay for quantitating the effects of in vivo drug treatments on murine neuromuscular disorders.

Animals↗
PubMed1992

Purification of a new galactanase from Penicillium oxalicum catalysing the hydrolysis of beta-(1----5)-galactofuran linkages.

An endo beta-(1----5)-galactofuranase from Penicillium oxalicum has been purified 91-fold. The enzyme is a basic glycoprotein with a pI 7.9 and 20% (w/w) carbohydrate content, galactose being the principal sugar. The apparent Mr of the enzyme estimated by denaturing gel electrophoresis was 77,000. The optimum pH was 5.0, and the enzyme was stable over the pH range 4.0-7.5. This enzyme hydrolyses specifically (1----5)-linked beta-D-galactofuranose residues in homo- and heterogalactans, but did not hydrolyse o-nitrophenyl galactose and beta-(1----5)-galactofuranbiose. Km and Vmax. values were 1.2 mg.ml-1 and 0.55 mumol.h-1 respectively when Eupenicillium crustaceum beta-(1----5)-galactofuran was used as substrate. The enzyme showed high affinity for different separation gels and proteins. The enzyme specificity and its mode of action showed that it could be an useful tool for analysing the fine structure of polysaccharides.

Carbohydrate Conformation↗
PubMed1991

Diurnal variations of rat liver enzymes catalyzing cholesterol ester hydrolysis.

Cholesterol ester hydrolase activity was determined at 3 h time intervals over 24 h in lysosomes, cytosol and microsomes from ad libitum-fed and 24 h food-deprived female rat liver. Diurnal rhythms were identified for the acid and neutral esterases, which were strikingly changed by fasting. In fed animals, lysosomal esterase specific activity exhibited a peak at noon and a sustained medium rate at early darkness, whereas total esterase was maximal at midnight. The circadian patterns of the cytosolic and the microsomal esterases paralleled each other, though the amplitude of rhythms differed, showing higher activities around midnight. After fasting, cholesterol esterase activity from all cell fractions reached a maximum near dark onset. These results are the first to indicate that cholesteryl ester hydrolysis may play a role in generating the diurnal rhythm of hepatic cholesterol.

Animals↗
PubMed1990

Neutral cholesteryl ester hydrolase in the rat lactating mammary gland: regulation by phosphorylation-dephosphorylation.

The characteristics of neutral cholesteryl ester hydrolase activities found in the microsomal and cytosolic subcellular fractions of rat lactating mammary tissue were investigated. The enzymes were assayed using cholesteryl oleate dispersed as a mixed micelle with phosphatidylcholine and sodium taurocholate (molar ratio 1:4:2) as substrate. This method gave activities approx. 20-fold higher than those seen when cholesteryl oleate was added in ethanol. Addition of phosphatidylcholine and sodium taurocholate to the assays using the ethanol-dissolved substrate did not increase the activities observed. When the cholesteryl oleate was dispersed with phosphatidylcholine only (molar ratio, 1:4) the activity of the two neutral cholesteryl ester hydrolases was also decreased considerably compared to that found with mixed micelles. In this case, however, approx. 60% of the cytosolic, but only 10% of the microsomal activity, was restored by separate addition of sodium taurocholate. The activities of both the microsomal and the cytosolic neutral cholesteryl ester hydrolases were inhibited by MgCl2, and this inhibition was almost completely reversed by the addition of an equimolar concentration of ATP. At a fixed concentration of MgCl2 increasing concentrations of ATP increased the enzyme activities in a dose-dependent way. The activity of the microsomal, but not the cytosolic enzyme was enhanced by a cyclic AMP-dependent protein kinase and both activities were inhibited by alkaline phosphatase (bovine milk). These results provide evidence for the regulation of neutral cholesteryl ester hydrolases in the rat lactating mammary gland by mechanisms involving phosphorylation-dephosphorylation and therefore suggest that these enzymes may be under hormonal control.

Adenosine Triphosphate↗
PubMed1990

Cholesterol ester cycle in rat liver: effects of estradiol and progesterone.

The regulation of the enzymatic synthesis and hydrolysis of cholesteryl esters by female sex hormones has been investigated in rat liver. When the effects of estradiol and progesterone were studied in "in vitro" incubations of hepatic microsomes, a dual effect was observed. Progesterone inhibited both microsomal cholesterol ester hydrolase and acyl-CoA: cholesterol acyltransferase activities in a concentration-dependent manner; however, the presence of estradiol stimulated cholesterol ester hydrolysis while it inhibited cholesterol ester formation. The administration of pharmacological doses of estradiol for three consecutive days resulted in decreased cytosolic and microsomal cholesterol esterase activities followed by an increased microsomal cholesteryl esters content whereas acyl-CoA: cholesterol acyltransferase and other microsomal parameters remained unchanged. Examination of the effects of the short-term treatment with pharmacological doses of progesterone showed that treatment was less effective in changing the hepatic pattern of the cholesteryl esters cycle, since only cytosolic cholesterol ester hydrolase activity diminished slightly. Neither cytosolic nor microsomal cholesterol esterase or acyl-CoA: cholesterol acyltransferase were consistently affected by the administration of therapeutical doses of estradiol or progesterone for 21 days, although both the free cholesterol-phospholipid and the total cholesterol-phospholipid molar ratios decreased moderately. The effect of the hormonal vehicle, propylene glycol, on some microsomal lipid parameters is finally discussed.

Acyl Coenzyme A↗
PubMed1990

Cephalosporin C acylase in the autolysis of filamentous fungi.

Cephalosporin C acylase activity was studied using fluorescamine determination of free--NH2 groups produced in the deacylation of cephalosporin C by the enzyme. Fourteen fungi from different genera were studied and low extracellular cephalosporin C acylase activity was found in the genera Aspergillus, Fusarium and Penicillium. Forty one fungi of these genera were checked but not all presented acylase activity. The enzyme was generally found to be an extracellular enzyme and during the process of autolysis its activity increased with incubation time and with increasing pH of the medium. In no case was beta-lactamase activity detected. Penicillium rugulosum and Penicillium griseofulvum were identified as good cephalosporin C acylase producers. Deacetyl esterase activity was also detected in these fungi.

Amidohydrolases↗
PubMed1989

Endochitinase from Aspergillus nidulans implicated in the autolysis of its cell wall.

An endochitinase from centrifuged autolyzed cultures of Aspergillus nidulans has been purified 100 times. The enzyme has Mw 27,000, pI of 4.8 units, pH optimum around 5 pH units. It is unstable at temperature greater than 70 degrees C and does not have a cation requirement. It is inhibited by Hg2+, Cu2+, Ca2+ and Ag+ and it does not have muramidase activity. The enzyme depolymerizes chitin rapidly with production of high molecular weight polysaccharides, and then slowly degrades these with production of N,N'-diacetylchitobiose. The enzyme hydrolyzes N,N',N''-triacetylchitotriose with production of N,N'-diacetylchitobiose and N-acetylglucosamine and this hydrolysis is inhibited by other chitin oligomers and N-acetylglucosamine. This enzyme hydrolyzes in the same way the chitin obtained from the cell wall of Aspergillus nidulans.

Aspergillus nidulans↗
PubMed1989

Determination of cephalosporin-C amidohydrolase activity with fluorescamine.

A spectrophotometric procedure for the assay of cephalosporin-C amidohydrolase activity, based on the determination of the 7-aminocephalosporanic acid (7-ACA) produced in the hydrolysis of cephalosporin-C by the enzyme, is described. This procedure can be used to detect 7-ACA over a range of 10 to 200 micrograms mL-1. The same method can be used as a fluorometric procedures with a 100-fold greater sensitivity. At pH 4.5 7-ACA produces a strong fluorophor with fluorescamine, detectable spectrophotometrically at 378 nm and fluorometrically at an excitation of 378 nm and emission of 495 nm. At this pH the fluorophors formed with cephalosporin-C, proteins and aminoadipic acid present minimal absorbance values. The conditions for maximal detection of 7-ACA in the presence of proteins, cephalosporin-C and aminoadipic acid have been determined.

Amidohydrolases↗
PubMed1987

Cardioplegia.

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Heart Arrest, Induced↗