Biomedical subjects

I Japundzić

Publications and source records attributed to I Japundzić.

At least 19 recordsLinked to original sources

PubMed1989

Selective decrease of duodenal phosphoprotein phosphatase activity is a general property of duodenal ulcerogens.

A phosphoprotein phosphatase (PPPase) is inhibited in rat duodenal mucosal cells very early after a single s. c. injection of the duodenal ulcerogens cysteamine, propionitrile and mepirizole. The effect seems to be independent of their effects on gastric acid secretion and on duodenal suppression of alkaline secretion. The enzyme inhibition is dose- and time-dependent under in vivo conditions. The inhibition of the PPPase activity is enzyme-selective at the level of mucosal cells in the duodenum. Under in vitro conditions, none of the duodenal ulcerogens inhibited PPPase activity. The results indicate that the effect of the ulcerogens on PPPase activity is probably exerted indirectly. When given simultaneously in vivo, propionitrile attenuated the inhibitory effects of cysteamine on the PPPase activity. However, both propionitrile and cysteamine potentiated the effect of mepirizole on PPPase depletion. These data indicate that cysteamine and propionitrile may act through the same mechanism when depleting PPPase activity. The mechanism of the decrease of duodenal protein phosphatase activity by mepirizole is probably different from the other duodenal ulcerogens.

Animals↗

PubMed1988

The influence of cysteamine and propionitrile on duodenal phosphoprotein phosphatase in rats.

Cysteamine and propionitrile cause severe duodenal ulcers with perforation within 24-48 h after a single injection in rats. These animal models were used to gain insight into the early, preulcerogenic biochemical changes in the duodenal mucosa. The results indicate that a single sc injection of cysteamine and propionitrile induced dose- and time-dependent decreases in the activity of phosphoprotein phosphatase (PPPase) in homogenate and particulate fractions of rat duodenal mucosa. The decrease in enzyme activity was detectable 4 h after the injection of the ulcerogens, it was maximal at 12 h, and hardly detectable at 24 h. No effect on the enzyme activity was found under in vitro conditions. PPPase activity in the liver was not influenced by either cysteamine or propionitrile. Furthermore, the toxic but nonulcerogenic derivative of cysteamine ethanolamine had no effect on PPPase in the duodenum. Thus, the effect of the duodenal ulcerogens on PPPase activity was indirect and organ specific, related only to the target organ (i.e., duodenal mucosa). The effect of the drugs was also selective at the level of mucosal cells: both duodenal ulcerogens depleted protein and alkaline phosphatase but not lysosomal acid phosphatase. The decrease of PPPase activity could be a general property of the duodenal ulcerogens since it is independent of their effect on endogenous somatostatin.

Acid Phosphatase↗

PubMed1988

Cobalt-dependent protein phosphatases from human cord blood erythrocytes. I. Submolecular structure and regulation of activity of E3 casein phosphatase.

We have identified three phosphoprotein phosphatases in the cytosol of human cord blood erythrocytes by sequential anion-exchange chromatography and gel filtration. The most abundant was E3 protein phosphatase. After rechromatography on a column of Ultrogel AcA-44 the enzyme had a molecular weight of 95,000 daltons. According to the data obtained by SDS/PAGE, the 95,000-dalton form was composed of non-identical subunits with a molecular mass of 23,000 and 16,000 daltons. Since ethanol decreased the molecular mass of the 95,000-dalton enzyme to 25,000 daltons, we suggest that the protein of 23,000-25,000 daltons represents the catalytic subunit. The decrease in the molecular weight is followed by a 2-fold increase in the Vmax value and by a change in kinetics: the negatively cooperative 95,000-dalton enzyme (h = 0.45) transforms into Michaelis-Menten kinetics (h = 1.0) in the 25,000-dalton form. Both molecular forms, 95,000 and 25,000 daltons, only dephosphorylated casein but not phosvitine and histones. Both forms were activated by CoCl2 and inhibited by organic, and most potently, by inorganic pyrophosphates to approximately the same degree. As opposed to the inorganic pyrophosphate, which affects the catalytic properties of the enzyme molecule, CoCl2 did not affect the catalytic properties of the enzymes, but it probably did affect the rate of 'E-S' complex formation. CoCl2 protected the 95,000-dalton enzyme from pyrophosphate inhibition. The data indicate that CoCl2 and pyrophosphate may take part in the regulation of the activity of both forms of E3 phosphatase.

Chromatography, Gel↗

PubMed1988

Cobalt-dependent protein phosphatases from human cord blood erythrocytes. II. Further characterization of E2 casein phosphatase.

Of three casein phosphatases isolated from the cytosol of human cord blood erythrocytes two were cobalt-dependent, E2 and E3. In the presence of CoCl2, E2 activity was the most prominent. In addition to casein, E2 dephosphorylated phosvitin and p-nitrophenyl phosphate (p-NPP) with pH optima at 6.8-7.2 for proteins and 9.0 for p-NPP. The native enzyme had a molecular weight of 104,000 daltons after AcA-44 Ultrogel filtration. According to SDS/PAGE it consisted of two subunits, 78,000 and 15,000 daltons. The 104,000-dalton form exhibited Michaelis-Menten kinetics and had the greatest affinity for casein between protein substrates tested. Ethanol denaturated the enzyme by 80%. Optimal activation of E2 phosphatase was achieved with 5 mmol/l CoCl2 which did not affect the catalytic properties of the enzyme but did affect the rate of 'E-S' complex formation. Inorganic pyrophosphate was not inhibitory for the 104,000-dalton enzyme. Judging by all these properties the natural substrate for E2 casein phosphatase could be P-pyruvate kinase.

Caseins↗

PubMed1987

Mechanism of action of cysteamine on duodenal alkaline phosphatase.

A single s.c. injection of cysteamine-HCl, a potent duodenal ulcerogen, drastically decreased duodenal alkaline phosphatase (DAP) activity in mucosal cells. The effect was detectable 4 hr after the injection of cysteamine, it was the most prominent at 12 hr and lasted less than 24 hr after the ulcerogen administration. Under the same experimental conditions cysteamine did not affect alkaline phosphatase activity in the liver. Furthermore, ethanolamine, the toxic but nonulcerogenic derivate of cysteamine, had no effect on the DAP activity if given in equimolar quantities. Thus, the effect of DAP activity seems to be a property of the duodenal ulcerogen, related only to the target organ, i.e. duodenal mucosa. Since cimetidine administration and pylorus ligation, which both abolish HCl hypersecretion provoked by cysteamine, did not "protect" the enzyme from the depletion, it is hard to believe that gastric acid hypersecretion could be responsible for the enzyme depletion provoked by the ulcerogen. Dopamine metabolism disorders, induced by cysteamine administration in the brain and duodenal mucosa, are not causally related to DAP-depletion either. Cysteamine most probably inhibits the DAP activity by three different mechanisms, by one acting directly on the enzyme molecules and by two others acting indirectly, through its adrenocorticolytic and stresogenic effects.

Adrenalectomy↗

PubMed1984

Characterization of low-molecular-weight acid phosphoprotein phosphatase associated with rat splenic cell nucleoli.

Evidence is presented on the existence of an acid phosphoprotein phosphatase (APPase) associated with rat splenic cell nucleoli. The enzyme is purified 1250-fold from 0.3 M NaCl nucleolar extract by means of chromatography on P cellulose and Sephacryl S-200. The nucleolar acid phosphoprotein phosphatase is a very basic protein (pI 8.3) and shows maximal activity at pH 5.8. It dephosphorylates acidic phosphoproteins (casein and phosvitin), ATP, and p-nitrophenyl phosphate, but not basic phosphoproteins (histones and protamine phosphate). The enzyme activity is very dependent on reducing agents, especially on ascorbic acid. Divalent and monovalent cations did not affect phosphatase activity, but heavier divalent metals, Co2+ and Zn2+, strongly inhibit the enzyme activity. The activity was also inhibited by N-ethylmaleimide, indicating a requirement for free sulfhydryl groups. The estimated molecular weight of the purified enzyme is approximately 38,000 by gel filtration and sedimentation in sucrose gradient concentration.

Animals↗

PubMed1984

Ontogenetic changes in protein dephosphorylating activity of the cytosolic compartment of rat erythrocytes.

Total casein phosphatase activity of erythrocytes from one-month-old rats was separated by DEAE-cellulose chromatography into three peaks--E1, E2 and E3--and only into two peaks--E1 and E3--when the erythrocyte donors were six- and 12-month-old rats. The activity of E1 (Mr 330 K) decreased continuously in erythrocytes during the first year of postnatal life. E2 (Mr 230 K) also decreased and completely disappeared from the cells of 12-month-old rats. E3 (Mr 180 K) was the dominant molecular form in the cytosol of erythrocytes during the first year of life. It decreased only up to six months of life. In this form E3 seems to be cooperative with respect to the substrate and to inhibitor molecules. The decrease of its kinetic parameters (Vmax and K0.55) was also found during postnatal ontogenesis. E3 isolated from erythrocytes of older rats (6 and 12 months) was more susceptible to inhibitory effect of pyrophosphate and to the change of ionic strength of eluting buffer than the enzyme from one-month-old rats. 0.2 mol.1(-1) NaCl lowered Mr of E3 phosphatase from 180 K to 128 K only in older rats.

Aging↗

PubMed1984

Chromatographic resolution and characterization of different casein phosphatase activities from the cytosolic compartment of rat erythrocytes.

Casein phosphatase activity in the cytosol of erythrocytes, taken from 1-month-old rats, is associated with three chromatographically distinct peaks: E1, E2 and E3. The dominant molecular form was E3 phosphatase, molecular weight 180,000 dalton, which increased in the cytosol of erythrocytes as compared to the value found in the same compartments of reticulocytes. The enzyme had the pH optimum at 6.5 and seemed to be positively cooperative with respect to substrate and negatively cooperative with respect to pyrophosphate, the most potent inhibitor. E1 and E2 casein phosphatases seem to be remnant activities in erythrocytes as compared to the values found in the cytosol of reticulocytes.

Animals↗

PubMed1978