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Biomedical subjects

J Hajdu

Publications and source records attributed to J Hajdu.

At least 91 records · Page 5Linked to original sources
PubMed1988

Effect of low-dose dopamine infusion on urinary prostaglandin E2 excretion in sick, preterm infants.

In pharmacological doses dopamine (DA) will interact with several endocrine systems and both inhibit (prolactin, thyrotropin) and enhance (renin, angiotensin) hormonal release. In this study we have examined whether DA given to preterm neonates will influence prostaglandin (PG) production. The question is of importance since vasodilator PGs play a role in postnatal adaptation. We determined the effect of low dose DA infusion on the 24 h urinary PGE2 excretion rate (an index of renal PGE2 synthesis) in preterm infants. Six preterm neonates, with a 24-h requirement of 2 micrograms/kg per min DA treatment for oedema, moderate oliguria, poor peripheral perfusion and/or mild systemic hypotension were studied on days 2 (Day 1), 3 (Day 2, the day of DA infusion), and 4 (Day 3, DA discontinued) of life. Six preterm infants (control group) that did not require DA infusion were also studied to monitor possible spontaneous changes in the renal PGE2 production on days 2, 3 and 4 of life. In the control group urine output (Uv) and PGE2 excretion rate remained unchanged during the study. In the study group DA administration resulted in nearly two-fold increases in both the Uv (194%) and PGE2 excretion (182%). Urinary PGE2 excretion was, however, closely related to urine flow in both the control infants (Day 1-3) and the study group infants (Day 1-2). Since increased diuresis stimulates renal PGE2 production, our data suggest that the increased PGE2 excretion on Day 2 in the study group was not due to a direct effect of DA on PGE2 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Dinoprostone↗
PubMed1988

X-ray Laue diffraction from crystals of xylose isomerase.

The Laue method (stationary crystal, polychromatic x-rays) was used to collect native and heavy-atom-derivative data on crystals of xylose isomerase (EC 5.3.1.5). These data were used to find the heavy-atom positions. The positions found by use of Laue data are the same as those found by use of monochromatic data collected on a diffractometer. These results confirm that Laue diffraction data sets, which can be obtained on a millisecond time scale, can be used to locate small molecules bound to protein active sites. The successful determination of heavy-atom positions also indicates that x-ray crystallographic data collected by the Laue method can be used to solve protein structures.

Aldose-Ketose Isomerases↗
PubMed1987

Pyridoxal phosphate site in glycogen phosphorylase b: structure in native enzyme and in three derivatives with modified cofactors.

The detailed environment of the essential cofactor pyridoxal 5'-phosphate in glycogen phosphorylase b, resulting from crystallographic refinement at 1.9-A resolution, is described. The pyridoxal ring is buried in a nonpolar site containing three aromatic rings while the 5'-phosphate group is highly solvated and makes only three direct contacts to the protein. The pyridine nitrogen interacts via a water with protein atoms [main chain carbonyl oxygen (Asn-133) and OH of tyrosine (Tyr-90)]. The crystal structures of three active derivatives of phosphorylase reconstituted with 5'-deoxypyridoxal 5'-methylenephosphonate (PDMP), 6-fluoropyridoxal 5'-phosphate (6-FPLP), and pyridoxal (PL) in place of the natural cofactor have been determined at 2.5-A resolution. The results for PDMP-phosphorylase show a closer proximity of the phosphonate group to the NZ atom of a lysine (Lys-574) than that observed in the native enzyme, consistent with 31P NMR studies that have shown a change in ionization state of the phosphonate group compared to the native cofactor phosphate. The replacement of the polar 5'-ester linkage by a CH2 group results in a small shift of a water and its hydrogen-bonded tyrosine (Tyr-648). In 6-FPLP-phosphorylase the fluorine is accommodated with no significant change in structure. It is suggested that substitution of the electronegative fluorine at the 6-position may result in lower activity of 6-FPLP-phosphorylase through a strengthening of hydrogen-bonded interactions to the pyridine nitrogen N1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Catalysis in the crystal: synchrotron radiation studies with glycogen phosphorylase b.

Direct observation of the progress of a catalysed reaction in crystals of glycogen phosphorylase b has been made possible through fast crystallographic data collection achieved at the Synchrotron Radiation source at Daresbury, UK. In the best experiments, data to 2.7 A resolution (some 108,300 measurements; 21,200 unique reflections) were measured in 25 min. In a series of time-resolved studies in which the control properties of the enzyme were exploited in order to slow down the reaction, the conversion of heptenitol to heptulose-2-phosphate, the phosphorylysis of maltoheptaose to yield glucose-1-phosphate and the oligosaccharide synthesis reaction involving maltotriose and glucose-1-phosphate have been monitored in the crystal. Changes in electron density in the difference Fourier maps are observed as the reaction proceeds not only at the catalytic site but also the allosteric and glycogen storage sites. Phosphorylase b is present in the crystals in the T state and under these conditions exhibits low affinity for both phosphate and oligosaccharide substrates. There are pronounced conformational changes associated with the formation and binding of the high-affinity dead-end product, heptulose-2-phosphate, which show that movement of an arginine residue, Arg 569, is critical for formation of the substrate-phosphate recognition site. The results are discussed with reference to proposals for the enzymic mechanism of phosphorylase. The feasibility for time-resolved studies on other systems and recent advances in this area utilizing Laue diffraction are also discussed.

Animals↗
PubMed1987

Influence of dopamine on atrial natriuretic peptide level in premature infants.

The role of dopamine (DA) in the activation and/or release of atrial natriuretic peptide (ANP) was investigated in 11 premature infants during the early postnatal period. Mean plasma concentration of ANP and free DA level before DA infusion was 252.6 +/- 210 fmol/ml, and 0.4 +/- 0.2 ng/ml, respectively. DA infusion in a dose of 2 micrograms/kg/min caused a rise in plasma free DA level to 59.7 +/- 21.5 ng/ml and a significant increase in GFR, diuresis, sodium excretion and fractional sodium excretion. The plasma concentration of ANP, however, remained unchanged (252.6 +/- 210.0 vs. 213 +/- 143.0 fmol/ml). Thus, our data failed to demonstrate a stimulatory effect of DA on ANP release in premature infants. The role of the high plasma concentration of ANP in preterm neonates immediately after birth has to be clarified.

Atrial Natriuretic Factor↗
PubMed1986

1-Stearyl,2-stearoylaminodeoxy phosphatidylcholine, a potent reversible inhibitor of phospholipase A2.

1-stearyl, 2-stearoylaminodeoxy phosphatidylcholine, a structurally modified phospholipid substrate analog exhibits potent and reversible inhibition of phospholipase A2 from cobra venom (N. naja naja). The apparent KI values determined in two different assay systems employing phosphatidylcholine-surfactant mixed micelles are in reasonable agreement (40 microM and 16 microM) and indicate that the inhibitor binds to the enzyme as much as two orders of magnitude more tightly than does dipalmitoyl phosphatidylcholine. With phosphatidylethanolamine as substrate, the kinetics are more complicated as the analog also exhibits activation, presumably at a second binding site on the enzyme.

Binding Sites↗
PubMed1986

Data on renal hypothermia by the venous passage.

The temperature values obtained in renal hypothermia through the venous circulation were biometrically analysed. It was found that there could be even about 4 degrees C temperature differences between the lower and upper poles of the kidney, always as large as 4 degrees C could be elicited in the first five minutes of hypothermia, the lower pole being colder. Similar but smaller differences were observed in ten minutes' hypothermia.

Animals↗
PubMed1985

Auto-alloplastics closure of cervical esophageal fistulae.

The authors performed auto-alloplastic replacement with flap through a round incision, 20 to 22 in mm diameter, to elaborate a suitable method for closing the fistulae which may from during cervical esophageal operations. Of the animals three died due to other causes, the others could be evaluated, and, although the operated esophagus had not been relieved from inner pressure, after 24 hours the animals were capable of drinking, later eating. The auto-alloplastic flap was followed up by histological examination for six months.

Animals↗
PubMed1984

Allosteric interactions of glycogen phosphorylase b. A crystallographic study of glucose 6-phosphate and inorganic phosphate binding to di-imidate-cross-linked phosphorylase b.

The binding to glycogen phosphorylase b of glucose 6-phosphate and inorganic phosphate (respectively allosteric inhibitor and substrate/activator of the enzyme) were studied in the crystal at 0.3 nm (3A) resolution. Glucose 6-phosphate binds in the alpha-configuration at a site that is close to the AMP allosteric effector site at the subunit-subunit interface and promotes several conformational changes. The phosphate-binding site of the enzyme for glucose 6-phosphate involves contacts to two cationic residues, Arg-309 and Lys-247. This site is also occupied in the inorganic-phosphate-binding studies and is therefore identified as a high-affinity phosphate-binding site. It is distinct from the weaker phosphate-binding site of the enzyme for AMP, which is 0.27 nm (2.7A) away. The glucose moiety of glucose 6-phosphate and the adenosine moiety of AMP do not overlap. The results provide a structural explanation for the kinetic observations that glucose 6-phosphate inhibition of AMP activation of phosphorylase b is partially competitive and highly co-operative. The results suggest that the transmission of allosteric conformational changes involves an increase in affinity at phosphate-binding sites and relative movements of alpha-helices. In order to study glucose 6-phosphate and phosphate binding it was necessary to cross-link the crystals. The use of dimethyl malondi-imidate as a new cross-linking reagent in protein crystallography is discussed.

Adenosine Monophosphate↗
PubMed1984

Cytotoxicity of platelet activating factor and related alkyl-phospholipid analogs in human leukemia cells, polymorphonuclear neutrophils, and skin fibroblasts.

A series of 11 alkyl-phospholipid analogs, structurally related to platelet activating factor (L-PAF), were analyzed for cytotoxic activity in human leukemic (HL-60) cells, human polymorphonuclear neutrophils, and Detroit 551 human skin fibroblasts. The order of selectiveness of the analogs in their cytotoxic response toward HL-60 cells in comparison to neutrophils is 1-alkyl-2-acetamide-GPC greater than 1-alkyl-2-methoxy-GPC greater than D-PAF greater than 1-acyl-2-lyso-GPC greater than 1-alkyl-2-lyso-GPC greater than L-PAF. A time-sequenced progression of events caused by the most potent cytotoxic alkyl-phospholipid analogs was characterized by (a) a rapid decrease in the cellular uptake and incorporation of 3H-thymidine into DNA that was detectable 4 hr after exposure to the analog, (b) a release of lactate dehydrogenase activity into the media at 8 hr after exposure, and (c) a decrease in cell number due to cell death that begins at 12 hr after exposure. Treatment of HL-60 cells with 1-alkyl-2-methoxy-GPC for 1 hr destroyed 40% of the cells after a subsequent 24-hr incubation period. The varied biologic activities of L-PAF, including how it affects serotonin release from platelets, blood pressure in rats, and cytotoxic responses in normal and leukemic cells, are discussed in relation to its D-enantiomer, 3-alkyl-2-acetyl-GPC, and the 2-acetamide analog. This report characterizes the kinetic events of the cellular responses in both normal and HL-60 cells in relation to the antineoplastic activities of unnatural ether-linked phospholipid analogs that are structurally related to L-PAF.

Antineoplastic Agents↗
PubMed1983

Pancreatic porcine phospholipase A2 catalyzed hydrolysis of phosphatidylcholine in lecithin-bile salt mixed micelles: kinetic studies in a lecithin-sodium cholate system.

Pancreatic porcine phospholipase A2 catalyzed hydrolysis of phosphatidylcholine in bile salt lecithin mixed micelles has been studied, utilizing a series of assay mixtures for which the micellar size, weight, and composition had been experimentally determined. Under these conditions the enzymatic hydrolysis is dependent on the phosphatidylcholine-to-sodium cholate molar ratio within the mixed micelle rather than the bulk concentration of the phospholipid in the mixture: at 5 mM phosphatidylcholine, variation of the NPC/NNaCh ratio from 0.2 to 2.0 increases the enzymatic activity from 82 to 933 mumol/min/mg protein. The initial rates are linear throughout the entire series of assay mixtures, the activity vs micellar concentration curves exhibit saturation behavior, and treatment of the data according to the "surface-as-cofactor" theory provides linear double-reciprocal plots which intersect in one point. The assay system should be applicable for detailed kinetic studies of lipolytic enzymes, including mammalian phospholipases which exhibit rather low activities toward lecithin-Triton X-100 mixed micelles. The system should also provide a convenient basis for mechanistic studies involving the use of inhibitory phospholipid substrate analogs.

Animals↗