PubMed Health⌕ Search

Biomedical subjects

L M van Golde

Publications and source records attributed to L M van Golde.

At least 109 records · Page 6Linked to original sources
PubMed1987

Phosphofructokinase in rat lung during perinatal development: characterization of subunit composition and regulation by fructose 2,6-bisphosphate and glucose 1,6-bisphosphate.

The subunit composition of phosphofructokinase (ATP: D-fructose-6-phosphate-1-phosphotransferase, EC 2.7.1.11) was studied in rat lung during perinatal development. No change in subunit composition during this period was observed. The three subunits of phosphofructokinase (L, M and C) were present in a ratio of approx. 65:25:10, respectively. In addition the levels of two effectors of phosphofructokinase were determined in rat lung during perinatal development: glucose 1,6-bisphosphate and fructose 2,6-bisphosphate. Until day 20 of gestation (term is 22 days) the glucose 1,6-bisphosphate level remains relatively constant (approx. 0.55 mumol/g protein), decreases before birth and increases sharply up to 1.04 mumol/g protein 2 days after birth. The amount of fructose 2,6-bisphosphate in rat lung shows a different developmental profile. A small peak is shown at day 17 of gestation whereas a larger peak up to 36.4 nmol/g protein is shown at days 20 and 21 of gestation. The time of maximal fructose 2,6-bisphosphate content corresponds with the time of glycogen breakdown and acceleration of surfactant synthesis in prenatal rat lung. Both glucose 1,6-bisphosphate and fructose 2,6-bisphosphate stimulate lung phosphofructokinase. Half maximal stimulations occur in the range of 24.1-70.9 microM glucose 1,6-bisphosphate and 0.17-0.34 microM fructose 2,6-bisphosphate.

Age Factors↗
PubMed1987

Effects of vasopressin on the synthesis of phosphatidylethanolamines and phosphatidylcholines by isolated rat hepatocytes.

The effect of vasopressin on the biosynthesis of phosphatidylcholines and phosphatidylethanolamines was investigated in freshly isolated rat hepatocytes in suspension. Treatment of hepatocytes with vasopressin inhibits the incorporation of [Me-14C]choline into phosphatidylcholines in a dose-dependent manner. The hormone does not affect the uptake, phosphorylation or oxidation of choline. Pulse-chase studies indicate that CTP:cholinephosphate cytidylyltransferase might be subject to hormonal regulation by vasopressin. In contrast with the inhibitory effect of vasopressin on the synthesis of phosphatidylcholines, this hormone stimulates the incorporation of [1,2-14C]ethanolamine into phosphatidylethanolamines in a dose-dependent manner. Pulse and pulse-chase studies with labelled ethanolamine show that the conversion of ethanolaminephosphate to CDPethanolamine as well as the formation of phosphatidylethanolamines from CDPethanolamine and diacylglycerol are enhanced. Determination of the effect of vasopressin on the activity of the enzymes of the synthesis de novo of phosphatidylethanolamines demonstrates an increase of the activity of ethanolaminephosphotransferase, probably as a result of the increased amount of diacylglycerol in vasopressin-treated cells.

Animals↗
PubMed1987

Hydrocortisone stimulates the development of oligodendrocytes in primary glial cultures and affects glucose metabolism and lipid synthesis in these cultures.

Cultures of glial cells were prepared from the brains of one-week-old rat pups. After one day in culture, serum was omitted from the medium and replaced by a combination of growth-stimulating hormones and other factors that enhanced the percentage of oligodendrocytes in the cultures. We investigated the effects of hydrocortisone on the development of oligodendrocytes, on the activities of oligodendrocyte-specific enzymes and on glucose- and lipid-metabolism of the glial cells. Hydrocortisone greatly enhanced the survival of glial cells in culture. The development of galactocerebroside-positive cells and the specific activity of 2',3'-cyclic-nucleotide 3'-phosphodiesterase were stimulated by 50 nM hydrocortisone, whereas these effects were partly reversed at higher concentrations of the hormone. The specific activity of glycerol-3-phosphate dehydrogenase was markedly stimulated by hydrocortisone; 1 microM or higher concentrations of hydrocortisone were required for an optimal effect. The consumption of glucose and the production of lactate were lowered by hydrocortisone whereas the oxidation of [6-14C]glucose to 14CO2 was not affected. Incorporation of [35S]sulfate into sulfolipids was greatly enhanced by hydrocortisone and [14C]incorporation from [1-14C]acetate into cholesterol and fatty acids was also stimulated but to a smaller extent. These results show that hydrocortisone exerts a general trophic function on glial cells in our culture system; enhances the ratio of oligodendrocytes over astrocytes, possibly by directing bipotential progenitor cells to develop into oligodendrocytes; specifically induces glycerol-3-phosphate dehydrogenase in oligodendrocytes.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1987

Aspects of metabolism and storage of pulmonary surfactant: experiments with isolated type II pneumocytes and lamellar bodies.

This review briefly summarizes our knowledge of the composition of pulmonary surfactant and the mechanisms involved in its biosynthesis. The currently available evidence suggests that dipalmitoylphosphatidylcholine, the major surface-active component of surfactant, can be synthesized in the alveolar type II pneumocyte via two pathways: (1) by direct synthesis de novo via the CPDcholine route, and (2) by remodelling of unsaturated phosphatidylcholines, most likely via a deacylation-reacylation mechanism. In addition, this paper focusses on recent findings concerning the biochemical characterization of lamellar bodies, the intracellular storage organelles of surfactant. Lamellar bodies from adult human lung contain a lamellar body-specific alpha-glucosidase--which should prove useful as a specific marker enzyme for this organelle.

Animals↗
PubMed1986

Glycerol 3-phosphate acylation in microsomes of type II cells isolated from adult rat lung.

Glycerol 3-phosphate acylation was studied in type II cells isolated from adult rat lung. The process was found to be largely microsomal. In the microsomes phosphatidic acid is the main product of glycerol 3-phosphate acylation. Glycerol-3-phosphate acyltransferase is rate limiting in the phosphatidic acid formation by the microsomes. Type II cell microsomes incorporate palmitoyl and oleoyl residues into phosphatidic acid at an equal rate if palmitoyl-CoA and oleoyl-CoA are added separately. However, if palmitoyl-CoA and oleoyl-CoA are added as an equimolar mixture the unsaturated fatty acyl moiety is incorporated much faster. Under the latter conditions monoenoic species constitute the most abundant products of glycerol 3-phosphate acylation. The microsomes incorporate both palmitoyl and oleoyl residues readily into both the 1- and 2-position of phosphatidic acid, even when palmitoyl-CoA and oleoyl-CoA are added together. Assuming that both phosphatidic acid phosphatase and cholinephosphotransferase do not discriminate against substrates with an unsaturated acyl moiety at the 1-position and a saturated acyl moiety at the 2-position, the last two observations indicate that a considerable percentage of phosphatidylcholine molecules synthesized de novo may have a saturated fatty acid at the 2-position and an unsaturated fatty acid at the 1-position, and that remodeling at the 1-position may be important for the formation of surfactant dipalmitoylphosphatidylcholine. They also indicate that type II cell microsomes are capable of synthesizing the dipalmitoyl species of phosphatidic acid. However, since there is a preference for the acylation of glycerol 3-phosphate with unsaturated fatty acyl residues, the percentage of dipalmitoyl species in the synthesized phosphatidic acid, and thereby the percentage of dipalmitoyl species in the phosphatidylcholine synthesized de novo, will probably depend on the relative availability of the various acyl-CoA species.

Acyl Coenzyme A↗
PubMed1986

Genetic relationship between lysosomal and lamellar body-specific alpha-glucosidases in human lung.

In lamellar bodies isolated from adult human lung at least two acid alpha-glucosidases are present: one similar to the lung lysosomal alpha-glucosidase, and another lamellar body-specific isoenzyme. In the present study we measured the activity of this lamellar body-specific alpha-glucosidase and of lysosomal alpha-glucosidase in a patient with an inherited deficiency of lysosomal alpha-glucosidase. The activity of the lamellar body-specific alpha-glucosidase was not affected in the patient, whereas the lysosomal alpha-glucosidase activity was strongly depressed. The results strongly suggest that the lysosomal alpha-glucosidase and the lamellar body-specific alpha-glucosidase are different gene products.

Concanavalin A↗
PubMed1986

Effects of triiodothyronine on the synthesis of sulfolipids by oligodendrocyte-enriched glial cultures.

Glial cultures were obtained from the brains of 1-week-old rats and were grown in a chemically defined, serum-free medium. We investigated the development of oligodendrocytes in these cultures and the synthesis of sulfolipids in the presence and absence of triiodothyronine (T3) in the medium: (1) In the presence of T3, the incorporation of [35S]sulfate into sulfolipids exhibited a developmental profile which is comparable to that found in the developing brain in vivo. A sharp peak of sulfolipid synthesis was observed at day 5 in vitro, which is equivalent to day 12 after birth. As observed in vivo, the percentage of label incorporated into sulfogalactosyldiradylglycerols decreased with time in culture. (2) Addition of T3 to the medium stimulated sulfolipid synthesis by oligodendrocytes in a dose-related manner (optimal T3 concentration, 30 nM). The hormone also enhanced the rates of cholesterogenesis and lipogenesis but to a lesser extent than sulfolipid synthesis. (3) The temporary omission of T3 from the medium resulted in lower rates of sulfolipid synthesis that could not be restored by readdition of T3. This inhibitory effect was most pronounced if the hormone was omitted from the medium on days 2 and 3 in culture. (4) Omission of T3 also resulted in the development of fewer oligodendrocytes in the cultures. Our results show that T3 is essential for the development of oligodendrocytes in our neurone-free culture system. They also indicate that the stimulation of myelination by thyroid hormones can, at least partially, be explained as a direct effect of T3 on oligodendrocytes, independent of an effect of T3 on neuronal growth.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1985

A specific acid alpha-glucosidase in lamellar bodies of the human lung.

In the present investigation, we have demonstrated that three lysosomal-type hydrolases, alpha-glucosidase, alpha-mannosidase and a phosphatase, are present in lamellar bodies isolated from adult human lung. The hydrolase activities that were studied, all showed an acidic pH optimum, which is characteristic for lysosomal enzymes. The properties of acid alpha-glucosidase in the lamellar body fraction and that in the lysosome-enriched fraction were compared. Using specific antibodies against lysosomal alpha-glucosidase from human placenta, two alpha-glucosidases could be distinguished in the lamellar body fraction: one with a high affinity to the antibodies as found in the lysosome-enriched fraction and another with a much lower affinity. Both forms showed an acidic pH optimum. The same heterogeneity of alpha-glucosidase in the lamellar body fraction could be observed using immobilized concanavalin A. The lectin was able to precipitate nearly all alpha-glucosidase activity of the lysosome-enriched fraction. In contrast, 30% of the alpha-glucosidase activity in the lamellar body fraction was not precipitable. Furthermore, the lamellar body alpha-glucosidase with the low antibody affinity could not be bound to concanavalin A. The results suggest that lamellar bodies contain at least two acid alpha-glucosidases: one similar to the lung lysosomal alpha-glucosidase, and another lamellar body-specific isoenzyme with a different immunoreactivity and lectin affinity. The lamellar body-specific alpha-glucosidase should prove useful as a lamellar body-specific marker enzyme.

Antibodies↗
PubMed1985

Activity and isoenzyme patterns of glycolytic enzymes during perinatal development of rat lung.

The enzymes hexokinase (EC 2.7.1.1), phosphofructokinase (EC 2.7.1.11), enolase (EC 4.2.1.11) and pyruvate kinase (EC 2.7.1.40) were studied in rat lung during development starting at day 16 of gestation (day-6) until 5 days after birth. During gestation, the activities of hexokinase type II, enolase and pyruvate kinase decreased and reached adult values at birth or shortly thereafter. Hexokinase type I remained relatively constant and the decrease of soluble type II hexokinase was compensated for by an increment of particle-bound hexokinase starting at day 20 of gestation until birth. In contrast, phosphofructokinase activity increased until day 20 of gestation followed by a rapid fall in activity until 2 days after birth. Except for hexokinase no isoenzyme shifts were observed in the period of observation. The results are discussed with respect to the proposed relationship between glycogen breakdown and surfactant synthesis during the perinatal period and suggest a regulatory role for phosphofructokinase in this process.

Animals↗
PubMed1985

Regulation and location of phosphatidylglycerol and phosphatidylinositol synthesis in type II cells isolated from fetal rat lung.

myo-Inositol decreases the synthesis of phosphatidylglycerol by type II cells isolated from fetal rat lung. Inositol addition also increases the synthesized amount of surfactant phosphatidylinositol. These observations indicate that at least part of the decreasing effect of inositol on phosphatidylglycerol formation is the result of competition between phosphatidylglycerol and phosphatidylinositol synthesis for a common pool of CDP diacylglycerol. Studies on the subcellular localization of enzymes measured under optimal conditions suggested that the enzymic activity required for the formation of phosphatidylglycerol is located mainly in the mitochondria, but most likely also for a small part in the endoplasmic reticulum, while the enzymic activity required for phosphatidylinositol formation is located in the endoplasmic reticulum. Inositol was found to inhibit glycerolphosphate phosphatidyltransferase in the microsomal fraction but not in the mitochondrial fraction derived from the type II cells, indicating that the competition between phosphatidylglycerol and phosphatidylinositol synthesis for CDP diacylglycerol takes place in the endoplasmic reticulum. This latter observation together with the observation of a switch-over from surfactant phosphatidylinositol to phosphatidylglycerol production around term indicate that the endoplasmic reticulum is the intracellular site of surfactant phosphatidylglycerol production.

Animals↗
PubMed1985

Lysophosphatidylcholine acyltransferase and lysophosphatidylcholine: lysophosphatidylcholine acyltransferase in alveolar type II cells from fetal rat lung.

The specific activity of lysophosphatidylcholine acyltransferase in sonicated fetal rat lung type II cells was found to be an order of magnitude greater than that of lysophosphatidylcholine:lysophosphatidylcholine acyltransferase. The specific activity of lysophosphatidylcholine acyltransferase in sonicated fetal rat lung type II cells increases towards the end of gestation, whereas that of lysophosphatidylcholine:lysophosphatidylcholine acyltransferase does not show a change. While lysophosphatidylcholine acyltransferase in whole fetal lung homogenate is more active towards oleoyl-CoA than towards palmitoyl-CoA, the enzyme in sonicated fetal type II cells is more active towards palmitoyl-CoA. If measured with palmitoyl-CoA as acyl donor, the specific activity of lysophosphatidylcholine acyltransferase in type II cells is higher than that in whole lung during late gestation. In contrast, the specific activity of lysophosphatidylcholine:lysophosphatidylcholine acyltransferase in type II cells is lower than that in whole lung. These observations indicate that in fetal rat type II cells the deacylation-reacylation cycle is more important for the formation of dipalmitoylphosphatidylcholine than the deacylation-transacylation process.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1985

Effects of ozone on phospholipid synthesis by alveolar type II cells isolated from adult rat lung.

Isolated alveolar type II cells were exposed to ozone by gas diffusion through the thin Teflon bottom of culture dishes. After exposure, type II cells were further incubated in the presence of labeled substrates to assess the capacity to synthesize surfactant lipids. The incorporation of [Me-14C]choline into both total and disaturated phosphatidylcholines in inhibited to 50% of the control values under conditions that result in a diffusion of 0.4 microgram O3/18 cm2-dish per 2.5 h. The incorporation rates of [1-14C]palmitate, [1-14C]acetate, D[U-14C]glucose, and [1,3-3H]glycerol into phosphatidylcholines are also lower after ozone exposure. Moreover, the synthesis of phosphatidylglycerols and phosphatidylethanolamines from these substrates is also inhibited by exposure of type II cells to ozone. These incorporation studies indicate that the effect of ozone is early in the biosynthetic pathway, probably at the step catalyzed by the enzyme glycerolphosphate acyltransferase. Determination of the activity of this enzyme after the ozone exposure shows that it is decreased, whereas the activity of lysophosphatidylcholine acyltransferase is increased. The activity of choline phosphotransferase also appears to be decreased after exposure of type II cells to ozone, although this enzyme was less susceptible than glycerolphosphate acyltransferase. Studies with the sulfhydryl reagent 5,5'-dithiobis (2-nitrobenzoic acid) indicate a positive correlation between the effect of this compound on enzyme activities in sonicated type II cells and the sensitivity of these enzymes in intact cells to ozone. This suggests that the effect of ozone on the synthesis of surfactant lipids is at least partially exerted via oxidation of the sulfhydryl groups of glycerolphosphate acyltransferase.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1984

Acetoacetate and glucose as substrates for lipid synthesis by rat brain oligodendrocytes and astrocytes in serum-free culture.

We have compared glucose and acetoacetate as precursors for lipogenesis and cholesterogenesis by oligodendrocytes and astrocytes, using mixed glial cultures enriched in oligodendrocytes. In order to differentiate between metabolic processes in oligodendrocytes and those in astrocytes, the other major cell type present in the mixed culture, we carried out parallel incubations with cultures from which the oligodendrocytes had been removed by treatment with anti-galactocerebroside serum and guinea-pig complement. The following results were obtained: 1. Both oligodendrocytes and astrocytes in culture actively utilize acetoacetate as a precursor for lipogenesis and cholesterogenesis. 2. In both cell types, the incorporation of acetoacetate into fatty acids and cholesterol exceeds that of glucose by a factor of 5-10 when the precursors are present at concentrations of 1 mM and higher. 3. Glucose stimulates acetoacetate incorporation into fatty acids and cholesterol, whereas acetoacetate reduces the entry of glucose into these lipids. This suggests that glucose is necessary for NADPH generation, but that otherwise the two precursors contribute to the same acetyl-CoA pool. 4. Both with acetoacetate and with glucose as precursor, oligodendrocytes are more active in cholesterol synthesis than astrocytes. 5. Using incorporation of 3H2O as an indicator for total lipid synthesis, we estimated that acetoacetate contributes one third of the acetyl groups and glucose one twentieth when saturating concentrations of both substrates are present.

Acetoacetates↗
PubMed1984

Synthesis of phosphatidylcholines in rat hepatocytes. Possible regulation by norepinephrine via an alpha-adrenergic mechanism.

The effect of norepinephrine on phosphatidylcholine and phosphatidylethanolamine formation was investigated in short-term incubations with freshly isolated rat hepatocytes. In the presence of dl-propranolol, norepinephrine decreases the incorporation of [methyl-14C]choline into phosphatidylcholines in a dose-dependent manner. At a concentration of 50 microM, norepinephrine (plus 20 microM propranolol) inhibits the incorporation of [methyl-14C]choline over a wide range of choline concentrations (59% inhibition at 5 microM choline; 34% inhibition at 1 mM choline). Norepinephrine also decreases the incorporation rates of [1-14C]palmitic acid and [1-14C]oleic acid into phosphatidylcholines. The effect of norepinephrine is mediated through an alpha-adrenergic receptor. Norepinephrine (plus propranolol) does not decrease the uptake or phosphorylation rate of [methyl-14C]choline. Pulse-label and pulse-chase studies indicate that the conversion rate of phosphocholine to CDP-choline, catalyzed by CTP:phosphocholine cytidylyltransferase, is diminished by norepinephrine. In contrast with the inhibitory effect of norepinephrine on phosphatidylcholine synthesis, this hormone stimulates the formation of phosphatidylethanolamines from [1,2-14C]ethanolamine. This increased incorporation rate is apparent at ethanolamine concentrations above 25 microM. A combination of norepinephrine and propranolol decreases, however, the synthesis of phosphatidylcholines from [1,2-14C]ethanolamine. The results indicate that alpha-adrenergic regulation dissociates the synthesis of phosphatidylcholines from that of phosphatidylethanolamines.

Animals↗
PubMed1984

Regulation of hepatic triacylglycerol synthesis and secretion.

Triacylglycerols are the most concentrated storage form of energy for the mammalian organism. These lipids are synthesized and secreted by the liver and serve as a fuel for other tissues. This paper presents a brief review of the regulation of hepatic triacylglycerol synthesis and secretion. Particular attention will be given to the dissociation of the synthesis of triacylglycerols from that of the metabolically closely related nitrogenous phospholipids. Recent evidence is presented which suggests that triacylglycerol synthesis (and secretion) is regulated, at least partially, at the diacylglycerol branchpoint.

Animals↗