Acyl-CoA oxidase from Candida tropicalis

Inhibition of acyl-CoA oxidase by phenol and its implication in measurement of the enzyme activity via the peroxidase-coupled assay system

Yeast (Candida tropicalis) acyl-CoA oxidase catalyzes the oxidation of a variety of acyl-CoA substrates to their corresponding alpha-beta enoyl-CoA products, with concomitant reduction of the buffer-dissolved O2 to H2O2. By utilizing indolepropionyl-CoA as a chromogenic substrate, we could measure the enzyme activity either directly by monitoring formation of the reaction product indoleacryloyl-CoA (lambda(max) = 367 nm) or indirectly by measuring the formation of H2O2 via the oxidative-coupled assay system, involving 4-aminoantipyrine, phenol, and horseradish peroxidase. We compared the rates of the enzyme catalysis by the above two methods. The experimental data revealed that the rate measured via the direct method was about twofold higher than that measured by the coupled-assay system. The above difference was found to be due to the inhibition of the enzyme by phenol, one of the reagents of the coupled assay system. The inhibitory role of phenol is not unique for indolepropionyl-CoA as substrate, but is also evident with aliphatic acyl-CoA substrates of varied chain lengths. Since the magnitude of inhibition is dependent on the nature of the acyl-CoA substrate, it is suggested that the coupled-reaction conditions must be carefully standardized with individual substrates. Some tips on standardizing the reaction conditions for quantitative measurement of the acyl-CoA oxidase-catalyzed reaction are offered.

Higher-plant medium- and short-chain acyl-CoA oxidases: identification, purification and characterization of two novel enzymes of eukaryotic peroxisomal beta-oxidation

Medium- and short-chain acyl-CoA oxidases were identified in and subsequently purified from dark-grown maize plantlets. The oxidase showing preference for medium-chain fatty acyl-CoAs (C10-C14) was purified to homogeneity. The oxidase showing preference for short-chain fatty acyl-CoAs (C4-C8) was purified over 150-fold. Various catalytic properties confirmed these enzymes to be true acyl-CoA oxidases. They produced trans-2-enoyl-CoA and H2O2 from the saturated acyl-CoA, as verified by various independent assay techniques. They also exhibited FAD-dependent activity; i.e. removal of loosely bound FAD by gel filtration markedly reduced activity, which could be restored upon re-addition of FAD. They showed apparent Km values between 2 and 10 microM for the acyl-CoA substrate giving maximal activity, no activity with the corresponding free fatty acid, high pH optima (8.3-8.6) and a peroxisomal subcellular location. The medium-chain acyl-CoA oxidase was determined to be a monomeric protein with a molecular mass of 62 kDa. The short-chain acyl-CoA oxidase was shown to have a native molecular mass of 60 kDa, but exhibited a labile multimeric structure, as indicated by the elution of multiple peaks of activity during several chromatographic steps, and ultimately by the purification of a subunit of molecular mass 15 kDa. The medium- and short-chain acyl-CoA oxidases were demonstrated to be distinct from the maize equivalent of the cucumber glyoxysomal long-chain acyl-CoA oxidase previously purified and characterized [Kirsch, Loffler and Kindl (1986) J. Biol. Chem. 261, 8570-8575]. The maize long-chain acyl-CoA oxidase was partially purified to permit determination of its substrate specificity; it showed activity with a broad range of acyl-CoAs of chain length greater than C8, and maximal activity with C16. The implications of the existence of multiple acyl-CoA oxidases in the regulation of plant peroxisomal beta-oxidation are discussed.

Effects of continuous medroxyprogesterone acetate on lipoprotein metabolism in postmenopausal women receiving estrogen

OBJECTIVE

To investigate the effects of medroxyprogesterone acetate (MPA) on the beneficial effects of estrogen therapy on lipid metabolism in postmenopausal women.

METHODS

Postmenopausal women were administered either conjugated equine estrogen (CEE) 0.625 mg daily for 3 months (Group 1) or CEE 0.625 mg in conjunction with MPA 2.5 mg (Group 2) or MPA 5.0 mg (Group 3) daily for 3 months. Plasma levels of cholesterol, triglyceride, lipoprotein lipids, apolipoproteins, sex steroid hormones and lecithin cholesterol acyltransferase activity (LCAT) were determined. Lipoprotein lipase (LPL) and hepatic triglyceride lipase (H-TGL) activities were measured in postheparin plasma. Changes in the lipid concentrations and enzymatic activities were evaluated in each group.

RESULTS

Total, low-density lipoprotein (LDL) cholesterol, apolipoprotein B concentrations and LCAT activity were all significantly reduced by treatment in the three groups. The levels of high-density lipoprotein (HDL), HDL2, and HDL3 cholesterol as well as the levels of apolipoprotein AI and AII were significantly elevated in groups 1 and 2. The mean decrease in these parameters was related to the dose of MPA. Levels of triglyceride in the HDL and HDL2 were significantly increased in group 1. The levels of triglyceride in plasma, very low density lipoprotein (VLDL), LDL, HDL3 and VLDL cholesterol and LPL activity were unaffected. H-TGL activity was significantly inhibited only in groups 1 and 2. MPA produced a dose-dependent increase in H-TGL activity. A significant negative correlation was observed between the HDL cholesterol concentration and H-TGL activity (r = 0.58 P < 0.001).

CONCLUSIONS

The administration of MPA 2.5 mg and 5.0 mg did not adversely affect the changes in VLDL-LDL metabolism produced by estrogen. However, MPA has dose-dependent negative effects on HDL metabolism by increasing H-TGL activity and the 5.0 mg MPA interferes with the favorable effects on lipids of estrogen in postmenopausal women.

Eicosapentaenoic acid, but not docosahexaenoic acid, increases mitochondrial fatty acid oxidation and upregulates 2,4-dienoyl-CoA reductase gene expression in rats

The aim of the present study was to investigate whether eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) was responsible for the triglyceride-lowering effect of fish oil. In rats fed a single dose of EPA as ethyl ester (EPA-EE), the plasma concentration of triglycerides was decreased at 8 h after acute administration. This was accompanied by an increased hepatic fatty acid oxidation and mitochondrial 2,4-dienoyl-CoA reductase activity. The steady-state level of 2,4-dienoyl-CoA reductase mRNA increased in parallel with the enzyme activity. An increased hepatic long-chain acyl-CoA content, but a reduced amount of hepatic malonyl-CoA, was obtained at 8 h after acute EPA-EE treatment. On EPA-EE supplementation, both EPA (20:5n-3) and docosapentaenoic acid (DPA, 22:5n-3) increased in the liver, whereas the hepatic DHA (22:6n-3) concentration was unchanged. On DHA-EE supplementation retroconversion to EPA occurred. No statistically significant differences were found, however, for mitochondrial enzyme activities, malonyl-CoA, long-chain acyl-CoA, plasma lipid levels, and the amount of cellular fatty acids between DHA-EE treated rats and their controls at any time point studied. In cultured rat hepatocytes, the oxidation of [1-14C]palmitic acid was reduced by DHA, whereas it was stimulated by EPA. In the in vivo studies, the activities of phosphatidate phosphohydrolase and acetyl-CoA carboxylase were unaffected after acute EPA-EE and DHA-EE administration, but the fatty acyl-CoA oxidase, the rate-limiting enzyme in peroxisomal fatty acid oxidation, was increased after feeding these n-3 fatty acids. The hypocholesterolemic properties of EPA-EE may be due to decreased 3-hydroxy-3-methylglutaryl-CoA reductase activity. Furthermore, replacement of the ordinary fatty acids, i.e., the monoenes (16:1n-7, 18:1n-7, and 18:1n-9) with EPA and some conversion to DPA concomitant with increased fatty acid oxidation is probably the mechanism leading to changed fatty acid composition. In contrast, DHA does not stimulate fatty acid oxidation and, consequently, no such displacement mechanism operates. In conclusion, we have obtained evidence that EPA, and not DHA, is the fatty acid primarily responsible for the triglyceride-lowering effect of fish oil in rats.

Chronic effect of hyperprolactinemia on blood glucose and lipid levels in mice

We studied the chronic effects of hyperprolactinemia, induced by ectopic pituitary grafting, on blood glucose and lipid levels in adult male mice. For one year after pituitary grafting, we measured the blood levels of prolactin, growth hormone (GH), insulin, glucose and free fatty acid (FFA) at various intervals. The graft caused consistent hyperprolactinemia without changes in the serum GH levels. Hypoglycemia developed at 1 and 3 months after grafting but was not accompanied by any changes of the serum insulin levels. Thereafter, the blood glucose and serum insulin levels began to increase in the pituitary-grafted (PG) mice, and at 12 months after the operation, both levels became significantly higher in PG mice than controls. The serum FFA levels and the weight of epididymal fat bodies were significantly lower in PG mice than controls from 3-12 months after the grafting. Thus, hyperprolactinemia leads to persistent hypolipidemia and biphasic changes in the blood glucose level.

Production of lactones and peroxisomal beta-oxidation in yeasts

Among aroma compounds interesting for the food industry, lactones may be produced by biotechnological means using yeasts. These microorganisms are able to synthesize lactones de novo or by biotransformation of fatty acids with higher yields. Obtained lactone concentrations are compatible with industrial production, although detailed metabolic pathways have not been completely elucidated. The biotransformation of ricinoleic acid into gamma-decalactone is taken here as an example to better understand the uptake of hydroxy fatty acids by yeasts and the different pathways of fatty acid degradation. The localization of ricinoleic acid beta-oxidation in peroxisomes is demonstrated. Then the regulation of the biotransformation is described, particularly the induction of peroxisome proliferation and peroxisomal beta-oxidation and its regulation at the genome level. The nature of the biotransformation product is then discussed (4-hydroxydecanoic acid or gamma-decalactone), because the localization and the mechanisms of the lactonization are still not properly known. Lactone production may also be limited by the degradation of this aroma compound by the yeasts which produced it. Thus, different possible ways of modification and degradation of gamma-decalactone are described.

Exercise metabolism during 1 hour of treadmill walking while taking high and low doses of propranolol, metoprolol, or placebo

Aerobic exercise and beta-blocking drugs are regularly prescribed as treatment for hypertension and as a prophylactic for patients at risk from coronary heart disease and for those recovering from an infarct. Some beta blockers, particularly non-beta 1-selective drugs, may make exercise more difficult, possibly by interfering with substrate metabolism during exercise. This study examined the effects of low and high doses of a beta 1-selective blocker, metoprolol, and a non-selective beta blocker, propranolol, on exercise metabolism. The study involved 20 healthy subjects (10 men, 10 women) who walked on a treadmill at 50% of their maximal oxygen uptake for 1 h on five occasions, separated by 7 days. On each of the five occasions they received one of the following treatments, given in random order: placebo, metoprolol 50 mg, metoprolol 100 mg, propranolol 40 mg, or propranolol 80 mg, all taken twice daily. Fat oxidation, expressed as a percentage of total energy expenditure, was significantly lower than with placebo for all of the active treatments except metoprolol 50 mg (placebo: 42.7 +/- 11.6%; metoprolol 50 mg: 38.7 +/- 14.1%, p = NS; metoprolol 100 mg: 36.3 +/- 13.7%, p = 0.05; propranolol 40 mg: 31.2 +/- 9.3%, p = 0.01; propranolol 80 mg: 29.5 +/- 10.9%, p = 0.01); and significantly lower with propranolol than with metoprolol (propranolol 40 mg: p = 0.0036; propranolol 80 mg: p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise metabolism in healthy volunteers taking atenolol, high and low doses of metoprolol CR/Z0K, and placebo

1. Exercise and beta-adrenoceptor blockade have important roles in the prevention and treatment of cardiovascular disease, but fatigue and a reduced capacity to exercise are commonly reported side effects of beta-adrenoceptor blockers. The reduced capacity to exercise may be partly caused by a reduction in fat metabolism. 2. We investigated the effects of atenolol 50 mg, metoprolol CR/Z0K 50 mg, metoprolol CR/Z0K 100 mg and placebo, on heart rate, energy expenditure, fat oxidation, plasma free fatty acids, glycerol, glucose, lactate, ammonia and perceived exertion during 2 h of treadmill walking at 40% of maximal oxygen uptake in 20 healthy volunteers. 3. Compared with placebo (38.0%), total fat oxidation was significantly lower on atenolol 50 mg (30.1%) and metoprolol CR/Z0K 100 mg (31.0%), but not on metoprolol CR/Z0K 50 mg (33.7%). Reductions in fat oxidation correlated well (r2 = 0.970) with reductions in exercising heart rate, and probably reflected the degree of beta 1-adrenoceptor blockade. Maximum plasma ammonia concentration was reached after 45 min of exercise on atenolol, 60 min on metoprolol CR/Z0K 100, and 75 min on metoprolol CR/Z0K 50, and was higher than placebo on all active drug treatments. 4. The greater reduction in fat oxidation with atenolol may be a reflection of a peak in plasma concentration, which is avoided with a controlled release preparation.

Near-stoichiometric interaction between the non-specific lipid-transfer protein of the yeast Candida tropicalis and peroxisomal acyl-coenzyme A oxidase prevents the thermal denaturation of the enzyme in vitro

A 14-kDa peroxisomal-matrix protein, named PXP-18, of the yeast Candida tropicalis is a structural and functional homologue of the mammalian nonspecific lipid-transfer protein (identical to sterol carrier protein-2). PXP-18 protected acyl-coenzyme A oxidase (ACO), the rate limiting enzyme of the peroxisomal beta-oxidation of fatty acids, from thermal inactivation at 48 degrees C or 70 degrees C. This effect was dose-dependent and not replaceable either by chicken egg white lysozyme, which is similar to PXP-18 (insofar as it is basic, small, and monomeric), or by bovine serum albumin, a carrier of lipids in the blood. ACO was irreversibly denatured by heat treatment at 70 degrees C for 15 min. However, when ACO and PXP-18 were similarly heat-treated, they formed a large complex at a molar ratio of PXP-18 to ACO subunit that was about one, independent of their initial ratio. This near-stoichiometric complex had ACO activity after a 500-fold dilution and was accompanied by ACO that was free of PXP-18 and indistinguishable from native ACO in size and activity. PXP-18 also protected urate oxidase, another peroxisomal enzyme, from inactivation at 66 degrees C for 15 min and facilitated the renaturation of ACO denatured by 2 M urea. These results indicated that PXP-18 is active in modulating the structure of peroxisomal enzymes in vitro. It is possible that PXP-18 functions as a stress protein or as a part of the system that keeps peroxisomal proteins intact.

Bovine ketosis and somatotrophin: risk factors for ketosis and effects of ketosis on health and production

Aspects of the metabolism and health of 63 cows which had been treated with different amounts of bovine somatotrophin (BST) daily in the preceding lactation and 25 control cows were studied. The aims of the study were first, to identify cows with ketotic conditions, either by measurements of blood metabolite concentrations or by clinical observations, secondly, to evaluate the risk of such conditions in cows treated with BST in the preceding lactation, and thirdly, to examine the metabolic and production consequences of the ketotic conditions in an environment in which the cows' health, body condition and nutrition were closely observed. The cows were categorised objectively by the use of cluster analysis into non-ketotic cows and ketonaemic cows, on the basis of their plasma metabolite concentrations. Twelve of the control cows and none of the cows previously treated with BST were classified as ketonaemic. Similarly, nine of the control cows but only two of the cows previously treated with BST had clinical ketosis. Some, but not all, of the decrease in the risk of clinical ketosis was attributable to the lower body condition score of the cows previously treated with BST. The clinically ketotic cows had a greater risk of other illness in the first 10 days post partum than their herdmates, but the ketonaemic cows had a significantly lower risk of other disease in the first 10 days post partum. The ketonaemic control cows were significantly heavier than the non-ketotic control cows, but they maintained a higher dry matter intake than the latter cows, probably a key factor in reducing the risk of clinical ketosis.

Large-scale purification and further characterization of rat pristanoyl-CoA oxidase

The elution of pristanoyl-CoA oxidase from butyl-Sepharose required unusually high concentrations of ethylene glycol, enabling the large-scale purification of this oxidase in a single chromatographic step. The enzyme, the native molecular mass of which was estimated previously at 415 kDa by gel filtration (Van Veldhoven, P.P., Vanhove, G., Vanhoutte, F., Dacremont, G., Eyssen, H. J. & Mannaerts, G. P. (1991) J. Biol. Chem. 266, 24676-24683), migrated as a 513-kDa protein during native gel electrophoresis. It showed a typical flavoprotein spectrum and probably binds 4 mol FAD/mol enzyme. Its amino acid composition was different from those of other known acyl-CoA oxidases. Screening of different rat tissues, either for enzyme activity or by immunoblotting, revealed the highest level of pristanoyl-CoA oxidase in liver, followed by kidney, intestinal mucosa, spleen and lung. The oxidase activities, measured with 2-methylpalmitoyl-CoA as the substrate, in livers from other vertebrates including man were low compared to rat. This was also confirmed by immunoblotting which provided a clear signal only in rat liver, possibly indicating that pristanoyl-CoA oxidase might be a rat-specific oxidase.

Photoaffinity labeling of acyl-CoA oxidase with 12-azidooleoyl-CoA and 12-[(4-azidosalicyl)amino]dodecanoyl-CoA

Synthesis of 32P-labeled CoA of high specific activity was achieved using partially purified dephospho-CoA kinase (EC 2.7.1.24) from pig liver with [gamma-32P]ATP as donor and dephospho-CoA as acceptor. A photoaffinity dodecanoic acid analog, 12-[(4-azidosalicyl)amino]dodecanoic acid was synthesized, as were its CoA derivative (ASD-CoA) and the CoA derivative of 12-azidooleic acid. The CoA derivatives were synthesized from azido fatty acid analogs by acyl-CoA synthetase. The synthesized photolabile reagents were tested as photoaffinity labels for acyl-CoA oxidase (EC 1.3.99.3) from Arthrobacter species. When a mixture of oxidase and the acyl-CoA analogs were incubated in the absence of ultraviolet light, the analogs were recognized as substrate. Acyl-CoA oxidase was incubated in the presence of acyl-CoA analogs and immediately photolyzed, which resulted in irreversible inhibition. Oleoyl-CoA and dodecanoyl-CoA protect the enzyme from photoactivated inhibition by 12-azidooleoyl-CoA and ASD-CoA, respectively. Analysis of photolyzed enzyme preparations by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed that both analogs preferentially labeled a 54,000 molecular weight protein. These results demonstrate that the photoaffinity acyl-CoA analogs have potential application as probes to identify and characterize lipid biosynthetic enzymes and to identify the active site of these proteins.

Effect of 3-thiadicarboxylic acid on lipid metabolism in experimental nephrosis

The effect of the sulfur-substituted fatty acid analogue 1,10 bis(carboxymethylthio)decane, also known as 3-thiadicarboxylic acid, on puromycin aminonucleoside-induced nephrotic hyperlipidemia was studied in rats. Treatment with 3-thiadicarboxylic acid (250 mg/kg) for 5 days reduced plasma levels of triglycerides from 5.8 to 2.7 mmol/L and cholesterol from 11.0 to 7.7 mmol/L. This was accounted for by decreases in very-low-density lipoprotein triglycerides, very-low-density lipoprotein cholesterol, and low-density lipoprotein cholesterol, without any major changes in the composition of plasma lipoproteins. The activities of two enzymes involved in fatty acid synthesis (ATP:citrate lyase and fatty acid synthetase) were inhibited by 3-thiadicarboxylic acid treatment, whereas acetyl-coenzyme A carboxylase activity was unchanged. In contrast, treatment with the sulfur-substituted fatty acid analogue induced the peroxisomal beta-oxidation of fatty acids ninefold and the mitochondrial beta-oxidation by 54% to 73%, depending on the substrate used. This was accompanied by a 26% reduction in hepatic triglyceride secretion rate. The hepatic phosphatidate phosphohydrolase activity was unchanged. 3-Thiadicarboxylic acid treatment suppressed the activity of the rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, by 58%, whereas hepatic LDL receptor expression was unaltered. The activities of lipoprotein lipase and hepatic lipase were unchanged by treatment. These results demonstrated that treatment with 3-thiadicarboxylic acid ameliorates hyperlipidemia in experimental nephrosis primarily by decreasing the overproduction of very-low-density lipoprotein present. The data also indicate that hepatic very-low-density lipoprotein synthesis and secretion is strongly influenced by the availability of the fatty acid substrate under the same hyperlipidemic conditions.

Early hormonal changes affect the catabolic response to trauma

OBJECTIVE

The authors sought to determine how temporary insulin suppression might alter the catabolic effects of cortisol, glucagon, and epinephrine.

SUMMARY BACKGROUND DATA

The metabolic responses to injury include hypermetabolism, accelerated net skeletal muscle protein breakdown, glucose intolerance, and insulin resistance. These alterations are associated with increased stress hormone concentrations. Insulin elaboration is usually suppressed immediately after an injury but is abundant later during convalescence. An infusion of hydrocortisone, glucagon, and epinephrine increases both stress hormone concentrations and insulin levels. It induces many of the metabolic alterations seen in critically ill patients, but it does not affect net muscle breakdown.

METHODS

Seven healthy adults received a stress hormone infusion for 3 days in two separate studies. During one study they, also received an infusion of the somatostatin analogue, octreotide (0.005 micrograms/kg/min), to suppress insulin elaboration for the first 24 hours. During the other study (control), insulin was permitted to rise unchecked.

RESULTS

Stress hormone concentrations, hypermetabolism (+/- 20% above basal), and leukocytosis were similar during both study periods. When insulin elaboration was temporarily suppressed, whole-body nitrogen loss was increased during the first 48 hours, and the efflux of amino acids from the forearm after 72 hours of infusion was 60% greater than the control level.

CONCLUSIONS

Temporary insulin suppression during physiologic increases in stress hormone concentrations amplified whole-body nitrogen loss and led to the development of accelerated net skeletal muscle protein breakdown. Early hormonal changes after an injury may affect the development of later catabolic responses.

The hypotriglyceridemic effect of eicosapentaenoic acid in rats is reflected in increased mitochondrial fatty acid oxidation followed by diminished lipogenesis

The effect of eicosapentaenoic acid (EPA) on fatty acid oxidation and on key enzymes of triglyceride metabolism and lipogenesis was investigated in the liver of rats. Repeated administration of EPA to normolipidemic rats resulted in a time-dependent decrease in plasma triglycerides, phospholipids and cholesterol. The triglyceride-lowering effect was observed after one day of feeding whereas lowering of plasma cholesterol and phospholipids was observed after five days of treatment. The triglyceride content of liver was reduced after two-day treatment. At that time, increased mitochondrial fatty acid oxidation occurred whereas mitochondrial and microsomal glycerophosphate acyltransferase was inhibited. The phosphatidate phosphohydrolase activity was unchanged. Adenosine triphosphate:citrate lyase, acetyl-CoA carboxylase, fatty acid synthetase and glucose-6-phosphate dehydrogenase were inhibited during the 15 d of EPA treatment whereas peroxisomal beta-oxidation was increased. At one day of feeding, however, when the hypotriglyceridemic effect was established, the lipogenic enzyme activities were reduced to the same extent in palmitic acid-treated animals as in EPA-treated rats. In cultured rat hepatocytes, the oxidation of [14C]palmitic acid to carbon dioxide and acid-soluble products was stimulated in the presence of EPA. These results suggest that the instant hypolipidemia in rats given EPA could be explained at least in part by a sudden increase in mitochondrial fatty acid oxidation, thereby reducing the availability of fatty acids for lipid synthesis in the liver for export, e.g., in the form of very low density lipoproteins, even before EPA induced peroxisomal fatty acid oxidation, reduced triglyceride biosynthesis and diminished lipogenesis.

Nocturnal oral glucose supplementation. The effects on protein metabolism in cirrhotic patients and in healthy controls

Nocturnal glucose administration might prevent gluconeogenesis and concomitant protein loss due to hepatic glycogen depletion. In this study the effects of nocturnal oral glucose supplements on nitrogen metabolism were investigated in 8 cirrhotic patients and in 8 healthy controls. During the night, either polymeric glucose was given or water as placebo. In the patients with cirrhosis on placebo, nitrogen balance was not different from controls: -63 +/- 8 vs. -55 +/- 4 mg N/kg b.wt./9 h (mean +/- SEM). Cirrhotic patients had increased nocturnal protein turnover rates (measured with 15N-glycine) and increased early morning levels of free fatty acids (FFA), lactate, insulin, glucagon and growth hormone. After glucose, nitrogen balance improved by 36% in the cirrhotic group, with a decrease in protein turnover rates and a decrease in plasma levels of beta-hydroxybutyrate, urea and glucagon. In the controls, glucose had no effects on nitrogen balance, on protein turnover or on the hormone levels, except for reduced FFA and ketone body levels. These data show that nocturnal calorie supplements improve nitrogen balance during the night in cirrhotic patients but not in healthy controls. Long interprandial intervals should be avoided in cirrhotic patients.

An in vitro reversible interconversion of rat liver fatty acid binding protein having different isoelectric points by virtue of the fatty acid content

Rat liver fatty acid binding protein (FABP) was purified to homogeneity by procedures including Sephadex G-100 and DEAE-cellulose column chromatographies. FABP was resolved into two major peaks, A and B, by the first DEAE-cellulose column chromatography. Each of these two fractions exhibited apparent homogeneity upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate with a molecular weight of 14,000 Da and amino acid analysis of these fractions has revealed that they are virtually identical or closely resemble each other. However, their fatty acid content was significantly different and heterogeneity was clearly demonstrated in the patterns of isoelectric focusing. In this communication, a single isoform (pI 5.0) from peak B FABP was further purified by successive DEAE-cellulose column chromatography and used as the final preparation. When the final FABP was partly freed of fatty acids by a mild delipidation technique using Lipidex 1,000, the pI shifted upward from 5.0 to 7.0. However, the pI of the delipidated FABP returned to its original pI of 5.0 after recombining fatty acids. These in vitro manipulations of bound fatty acid content made clear its possible cause of the microheterogeneity of FABP.

Time series cross-correlation analysis of postparturient relationships among serum metabolites and yield variables in Holstein cows

Time series cross-correlation analysis was used to determine relationships among serum beta-hydroxybutyrate, glucose, FFA, cholesterol, milk yield, DMI, and estimated net energy balance for 42 d postpartum for 14 multiparous cows. Milk yield was positively associated with beta-hydroxybutyrate concentrations on the same day, and milk yield was a primary determinant of metabolic change. Dry matter intake was negatively correlated with beta-hydroxybutyrate concentrations 3 d later and on the same day. The data supported in vitro studies showing that FFA are positively associated with beta-hydroxybutyrate production, showed that glucose concentrations are negatively cross-correlated with beta-hydroxybutyrate concentrations, and found that estimated net energy balance is negatively cross-correlated with beta-hydroxybutyrate. Analyses suggested that serum glucose and cholesterol concentrations significantly decreased with increased milk yield; analyses also suggested that elevated beta-hydroxybutyrate concentrations were associated with decreases in milk yield 6 d later. beta-Hydroxybutyrate and FFA concentrations 3 to 9 d before parturition were positively related to cholesterol concentrations, and relationships were positive between estimated net energy balance and cholesterol, suggesting that cholesterol concentrations increased as precursors for cholesterol synthesis were available. Time series cross-correlation analysis was a useful tool in examining relationships among variables when repeated samples were obtained from the same individuals.

Interrelationships of bile acid and phospholipid fatty acid species with cholesterol saturation of duodenal bile in health and gallstone disease

The relative amount of cholesterol and the fatty acid composition of phosphatidylcholines in bile can be influenced by the bile acid species secreted. To search for a contribution of secondary bile acids and of phosphatidylcholines to supersaturation of bile in gallstone disease, we compared the relative amount of cholesterol and the biliary composition of bile acids and of phospholipid fatty acids in cholecystokinin-stimulated duodenal bile of 22 female gallstone patients and 16 healthy controls and analyzed the interrelationships of these bile constituents. Gallstone patients had higher molar percentages of cholesterol than did controls (10.2 +/- 3.2 vs. 6 +/- 1.5 mol%; p less than 0.001) and demonstrated a trend toward larger fractions of deoxycholic and lithocholic acids. By linear models, variation of cholesterol saturation could be predicted (p less than 0.001) up to 53% by the bile acid pattern and up to 81% by the fatty acid pattern of phospholipids. Linear path analysis (goodness-of-fit index = 0.973) confirmed the tight relationship between phospholipid fatty acids (positive: oleic, arachidonic; negative: linoleic, palmitoleic) and the relative amount of cholesterol; more than half the influence of cholic, deoxycholic and lithocholic acids on the relative amount of cholesterol could be explained indirectly by their influence on the phospholipid fatty acid pattern. We conclude that the relationships examined by path analysis support the working hypothesis that secondary bile acids contribute to supersaturation of bile mainly by changing the fatty acid pattern of the secreted phospholipids (presumably the pattern of phosphatidylcholines), which increases the molar ratio of cholesterol/phospholipids in bile.

Postparturient metabolic and production responses in cows previously exposed to long-term treatment with somatotropin

Postparturient metabolic and production responses were studied for 85 multiparous cows consisting of controls and animals that had been previously exposed to long-term treatment with bST. Older cows previously exposed to bST at high doses (51.6 mg/d) had lower milk yields than controls. However, there were no significant differences compared with controls in milk yield for lower dose (17.2 mg/d) older cows or parity 2 cow groups. The bST-treated groups had higher postpartum DMI, lower serum FFA, lower serum beta-hydroxybutyrate levels, and higher serum glucose than controls. Some bST-exposed groups had lower milk fat but higher milk protein levels. All bST-treated groups had significantly lower ratios of C18 to C4 to 10 milk fatty acids. Control cows of both parity groups were in higher body condition and weighed more than bST-treated cows prior to calving. The differences in postpartum metabolism may be attributed to differences in body composition resulting from bST treatment in the prior lactation, because use of body condition score prior to calving as a covariate did not substantially alter responses. The control cows probably had greater reserves of mobilizable lipid. These contentions are supported by changes in milk composition for bST-treated cows, which were consistent with animals of greater appetite, mobilizing less lipid. The bST-treated cows were probably more energetically efficient milk producers because they produced milk from feed rather than from mobilization of tissue stores. These data suggest that bST use in a prior lactation may have potential benefit in reducing risk of metabolic disorders associated with lipid mobilization in the postparturient period.

Determination of Candida tropicalis acyl coenzyme A oxidase isozyme function by sequential gene disruption

A recently developed transformation system has been used to facilitate the sequential disruption of the Candida tropicalis chromosomal POX4 and POX5 genes, encoding distinct isozymes of the acyl coenzyme A (acyl-CoA) oxidase which catalyzes the first reaction in the beta-oxidation pathway. The URA3-based transformation system was repeatedly regenerated by restoring the uracil requirement to transformed strains, either through selection for spontaneous mutations or by directed deletion within the URA 3 coding sequence, to permit sequential gene disruptions within a single strain of C. tropicalis. These gene disruptions revealed the diploid nature of this alkane- and fatty acid-utilizing yeast by showing that it contains two copies of each gene. A comparison of mutants in which both POX4 or both POX5 genes were disrupted revealed that the two isozymes were differentially regulated and displayed unique substrate profiles and kinetic properties. POX4 was constitutively expressed during growth on glucose and was strongly induced by either dodecane or methyl laurate and to a greater extent than POX5, which was induced primarily by dodecane. The POX4-encoded isozyme demonstrated a broad substrate spectrum in comparison with the narrow-spectrum, long-chain oxidase encoded by POX5. The absence of detectable acyl-CoA oxidase activity in the strain in which all POX4 and POX5 genes had been disrupted confirmed that all functional acyl-CoA oxidase genes had been inactivated. This strain cannot utilize alkanes or fatty acids for growth, indicating that the beta-oxidation pathway has been functionally blocked.

Determination of Candida tropicalis acyl coenzyme A oxidase isozyme function by sequential gene disruption

A recently developed transformation system has been used to facilitate the sequential disruption of the Candida tropicalis chromosomal POX4 and POX5 genes, encoding distinct isozymes of the acyl coenzyme A (acyl-CoA) oxidase which catalyzes the first reaction in the beta-oxidation pathway. The URA3-based transformation system was repeatedly regenerated by restoring the uracil requirement to transformed strains, either through selection for spontaneous mutations or by directed deletion within the URA 3 coding sequence, to permit sequential gene disruptions within a single strain of C. tropicalis. These gene disruptions revealed the diploid nature of this alkane- and fatty acid-utilizing yeast by showing that it contains two copies of each gene. A comparison of mutants in which both POX4 or both POX5 genes were disrupted revealed that the two isozymes were differentially regulated and displayed unique substrate profiles and kinetic properties. POX4 was constitutively expressed during growth on glucose and was strongly induced by either dodecane or methyl laurate and to a greater extent than POX5, which was induced primarily by dodecane. The POX4-encoded isozyme demonstrated a broad substrate spectrum in comparison with the narrow-spectrum, long-chain oxidase encoded by POX5. The absence of detectable acyl-CoA oxidase activity in the strain in which all POX4 and POX5 genes had been disrupted confirmed that all functional acyl-CoA oxidase genes had been inactivated. This strain cannot utilize alkanes or fatty acids for growth, indicating that the beta-oxidation pathway has been functionally blocked.

The reductive half-reaction in acyl-CoA oxidase from Candida tropicalis: interaction with acyl-CoA analogues and an unusual thioesterase activity

A series of acyl-CoA analogues has been used to probe the substrate binding site and reductive half-reaction of acyl-CoA oxidase from the alkane utilizing yeast Candida tropicalis. Alkyl-SCoA thioethers, from octyl- to hexadecyl-SCoA, bind to the oxidase with progressively larger spectral perturbation of the flavin chromophore and with an incremental binding energy of about 260 cal/methylene group. The hydrocarbon binding subsite for acyl-CoA oxidase appears extensive and only weakly hydrophobic. CoA binding per se appears to contribute about 2.8 kcal to the observed binding energy. A number of acyl-CoA analogues such as 3-thia-acyl-, 3-oxa-acyl-, trans-3-enoyl-, and 3-keto-acyl-CoA derivatives form charge transfer complexes with the oxidase, but these long wavelength bands are both less pronounced and much less stable than those encountered with the acyl-CoA dehydrogenases. This instability reflects an intrinsic thioesterase activity of the oxidase which is observed with those ligands forming enolate to oxidized flavin charge-transfer complexes, but not with normal substrates such as palmitoyl-CoA. Chemical precedent suggests that these enzyme-bound enolates eliminate CoA via a ketene intermediate. The differences in behavior between acyl-CoA oxidase and dehydrogenase toward the ligands used in this work are discussed in terms of the need to exclude oxygen from productive encounters with substrate-reduced dehydrogenase.

Reciprocal changes of plasma glucose and ketone bodies in fasted and acutely diabetic rats after CNS stimulation

To assess the effect of chemical stimulation of the central nervous system (CNS) on ketogenesis, we injected neostigmine (5 x 10(-8)mol) into the third cerebral ventricle in normal rats fasted for 48 h and fed rats with diabetes induced by streptozotocin (STZ, 80 mg/kg). The hepatic venous plasma levels of ketone bodies (3-hydroxybutyrate and acetoacetate), free fatty acids (FFA), and glucose were measured for 120 min after the injection of neostigmine under pentobarbital anesthesia. In the normal rats, plasma glucose levels were significantly increased but neither ketone bodies nor FFA were affected by CNS stimulation with neostigmine. In contrast the plasma levels of ketone bodies and FFA were significantly increased in STZ-diabetic rats, while glucose levels remained unchanged. The intravenous infusion of somatostatin (1.0 microgram/kg/min) suppressed the increase in plasma ketone bodies following CNS stimulation in STZ-diabetic rats. These findings suggest that CNS stimulation with neostigmine may accelerate ketogenesis by promoting the lipolysis, which may be induced by glucagon, in fed diabetic rats but not in normal fasted rats.

Changes in carbohydrate metabolism in association with glipizide treatment of type 2 diabetes

Nineteen patients with Type 2 diabetes were treated with glipizide for 2.5-6 months, and measurements made of metabolic variables before and after glipizide treatment. For purposes of analysis, the glipizide associated decrease in fasting plasma glucose concentration was used to divide patients into 'good' responders (decrease of 4.0 mmol l-1 or more, n = 9) or 'fair' responders (decrease of 3.0 mmol l-1 or less, n = 10). Good responders had a significantly greater fall in their mean (+/- SE) hourly plasma glucose (6.3 +/- 0.6 vs 2.7 +/- 0.3 mmol l-1, p less than 0.001) and NEFA (164 +/- 40 vs 60 +/- 37 mumol l-1, p less than 0.05) concentrations from 0800 to 1600 h in response to meals (0800 and 1200 h) than did the fair responders. However, the increase in hourly plasma insulin concentration following glipizide treatment was the same in the good (323 +/- 103 to 413 +/- 124 pmol l-1) and fair (276 +/- 42 to 345 +/- 43 pmol l-1) responders.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute changes in plasma non-esterified fatty acid concentration do not change hepatic glucose production in people with type 2 diabetes

The effect of changes in plasma non-esterified fatty acid concentration (NEFA) on plasma glucose concentration, hepatic glucose production (Ra), and glucose disposal (Rd) rates was determined in 14 patients with Type 2 diabetes. Seven patients had relatively mild fasting hyperglycaemia (less than 10.0 mmol l-1), whereas the remaining seven had relatively severe fasting hyperglycaemia (greater than 14.0 mmol l-1). Each patient was infused from 2000 to 0800 h with 3-3H-glucose on two occasions, with or without neutral fat emulsion and heparin (mild hyperglycaemia group), or with or without nicotinic acid (severe hyperglycaemia group). Plasma NEFA concentration increased from 0.33 +/- 0.06 (+/- SE) to 4.78 +/- 0.42 mmol l-1 in response to the lipid and heparin infusion, but plasma glucose concentration (7.8 +/- 0.7 vs 7.4 +/- 0.8 mmol l-1), Ra (0.44 +/- 0.02 vs 0.46 +/- 0.02 mmol m-2 min-1), and Rd (0.42 +/- 0.02 vs 0.46 +/- 0.02 mmol m-2 min-1) were unchanged. Nicotinic acid decreased plasma NEFA concentration from 0.54 +/- 0.15 to 0.23 +/- 0.08 mmol l-1, but plasma glucose (15.0 +/- 1.0 vs 15.5 +/- 1.4 mmol l-1), Ra (0.74 +/- 0.07 vs 0.68 +/- 0.07 mmol m-2 min-1), and Rd (0.73 +/- 0.07 vs 0.68 +/- 0.07 mmol m-2 min-1) were unchanged. The results indicate that acute changes in plasma NEFA concentration did not lead to any change in overnight glucose production or disposal rates.

Perfluoro-N-decanoic acid effects on enzymes of fatty acid metabolism

In vitro perfluorodecanoate (PFDA) effects on Pseudomonas acyl-CoA synthetase, Candida acyl-CoA oxidase and pigeon muscle carnitine acetyltransferase were examined. Synthetase made little PFDA-CoA from PFDA. It used palmitate, oleate, laurate and decanoate more extensively. PFDA inhibited acyl-CoA formation from these acids. Palmitoyl-CoA formation was affected most. That of decanoyl-CoA was affected least. Inhibitions appeared to be competitive. Acyl-CoA oxidase test substrates were palmitoyl-CoA, lauroyl-CoA and decanoyl-CoA. Oxidase preferred C-10 and C-12 acyl-CoAs. PFDA inhibited oxidation of C-10 and C-12 acyl-CoAs more than that of palmitoyl-CoA. Inhibitions with C-16 and C-10 acyl-CoAs were competitive, KIs 593 +/- 150 and 76 +/- 6.0 microM. Acetyl-CoA was the best acetyltransferase substrate. C-2 to C-8 transfer from acyl-CoAs was inhibited similarly by PFDA. Inhibitions of C-2 and C-8 transfer were competitive and non-competitive, respectively, KIs 111 +/- 15 and 76 +/- 28 microM.

Effect of acute hyperglycemia on plasma triglyceride concentration and triglyceride secretion rate in non-fasted rats

The effect of an intravenous infusion of glucose on plasma triglyceride (TG) concentration in fed rats was determined in order to partially elucidate the mechanism of diabetes-induced hypertriglyceridemia. Glucose infused at 8 mg/kg per min caused the plasma TG concentration to be elevated significantly when compared to controls infused with saline alone. In rats which were euglycemic (clamped, insulin infused at 2.5 mU/kg per min), plasma TG concentration remained constant throughout the glucose infusion period (8 mg/kg per min). Hyperglycemic rats infused with insulin (2.5 mU/kg per min) as well as with glucose (16 mg/kg per min) were also hypertriglyceridemic. Infusion of insulin alone did not change the concentration of plasma TG over a 150 min period. Glucose was also infused (8 mg/kg per min) with somatostatin (1 micrograms/kg per min) to block endogenous production of insulin. Somatostatin infusion did not suppress glucose-induced hypertriglyceridemia. For all treatments, the net change in TG concentration was found to positively correlate with the net change in plasma glucose concentration at 150 min after the infusions (r = 0.83, P less than 0.001). The higher TG concentration in the glucose infused, hyperglycemic clamp and glucose plus somatostatin groups reflected an increased rate of TG secretion, in the presence of a lower concentration of plasma free fatty acids. These results suggest that in a non-fasted state, acute hyperglycemia increases plasma TG by stimulating hepatic TG secretion, in a manner which is independent of either plasma insulin or free fatty acids levels.

A novel peroxisomal nonspecific lipid-transfer protein from Candida tropicalis. Gene structure, purification and possible role in beta-oxidation

We have sequenced the nucleotides of the gene POX18 that encodes PXP-18, a major peroxisomal polypeptide inducible by oleic acid in the yeast Candida tropicalis. POX18 had a single open reading frame of 127 amino acids. Some 33% of the amino acid sequence of the predicted basic polypeptide (13,805 Da), was identical to that of the nonspecific lipid-transfer protein (sterol carrier protein 2) from rat liver. PXP-18, purified to near homogeneity from isolated peroxisomes, had an amino-terminal sequence identical to that of the predicted polypeptide except for the initiator methionine, and had nonspecific lipid-transfer activity comparable to that of its mammalian equivalents. Unexpectedly, PXP-18 lacked the cysteine residue thought to be essential for the activity of this protein in mammals. RNA blot analysis showed that the POX18 gene was expressed exclusively in cells grown on oleic acid, suggesting that PXP-18 has a role in the beta-oxidation of long-chain fatty acids. PXP-18 modulated acyl-coenzyme A oxidase activity at low pH.

The effect of Acipimox on triacylglycerol metabolism in rat

The mechanism behind the hypolipidaemic effect of the drug Acipimox was studied in rat. The triacylglycerol (TG) lowering effect of the drug was accompanied by a marked reduction in free fatty acid (FFA) levels in the plasma. Also, the flux of TG from the liver to the plasma was substantially reduced. The liver TG content was not significantly changed. No significant effect of Acipimox treatment on the activities of glycerol 3-phosphate acyltransferase, phosphatidate phosphohydrolase or diacylglycerol acyltransferase in rat liver was observed. These findings strongly support the contention that Acipimox exerts its TG-lowering effect mainly by reducing FFA influx to the liver and thereby reducing the de novo biosynthesis of TG in the liver.

Catabolic defect of triglyceride is associated with abnormal very-low-density lipoprotein in experimental nephrosis

Very-low-density lipoprotein (VLDL)-triglyceride (TG) kinetics were examined in puromycin aminonucleoside-induced nephrotic rats in order to establish the nature of the hypertriglyceridemia associated with this condition. Nephrotic rats had a plasma TG concentration 10-fold higher than the controls. In nephrotic rats TG secretion rate was elevated only 1.2-fold above the controls, suggesting that the catabolism of TG was also impaired. Lipolytic activities were determined in postheparin plasma (PHP) of the control and the nephrotic rats. There were no significant differences in either the activity of lipoprotein lipase (LPL) or hepatic lipase (HL). VLDL-TG was endogenously radiolabeled in donor rats with [2-3H]-glycerol. The half life (T1/2) was then determined by monitoring the clearance of plasma [3H]-VLDL-TG in normal recipient animals. The T1/2 of VLDL-TG from nephrotic rats was twice that of normal rats. The defect in VLDL-TG clearance could be partially rectified by preincubation with high-density lipoprotein (HDL) from normal rats, but not with HDL from nephrotic rats. VLDL from either nephrotic or normal rats were incubated with PHP of normal rats to assess the effectiveness of VLDL-TG as a substrate for PHP. The lipolytic rate for nephrotic VLDL was significantly lower than that for normal VLDL, suggesting that VLDL from nephrotic rats was somewhat resistant to the action of LPL and HL. When VLDL from nephrotic rats was preincubated with HDL from normal rats, the low lipolytic rate of VLDL-TG improved significantly. This was not observed when HDL from nephrotic rats was used for the preincubation. The results suggested that physical and/or chemical change of VLDL particles due to nephrosis results in a catabolic defect of VLDL-TG.

Nibbling versus gorging: metabolic advantages of increased meal frequency

We studied the effect of increasing the frequency of meals on serum lipid concentrations and carbohydrate tolerance in normal subjects. Seven men were assigned in random order to two metabolically identical diets. One diet consisted of 17 snacks per day (the nibbling diet), and the other of three meals per day (the three-meal diet); each diet was followed for two weeks. As compared with the three-meal diet, the nibbling diet reduced fasting serum concentrations of total cholesterol, low-density lipoprotein cholesterol, and apolipoprotein B by a mean (+/- SE) of 8.5 +/- 2.5 percent (P less than 0.02), 13.5 +/- 3.4 percent (P less than 0.01), and 15.1 +/- 5.7 percent (P less than 0.05), respectively. Although the mean blood glucose level and serum concentrations of free fatty acids, 3-hydroxybutyrate, and triglyceride were similar during both diets, during the nibbling diet the mean serum insulin level decreased by 27.9 +/- 6.3 percent (P less than 0.01) and the mean 24-hour urinary C-peptide output decreased by 20.2 +/- 5.6 percent (P less than 0.02). In addition, the mean 24-hour urinary cortisol excretion was lower by 17.3 +/- 5.9 percent (P less than 0.05) at the end of the nibbling diet than at the end of the three-meal diet. The blood glucose, serum insulin, and C-peptide responses to a standardized breakfast and the results of an intravenous glucose-tolerance test conducted at the end of each diet were similar. We conclude that in addition to the amount and type of food eaten, the frequency of meals may be an important determinant of fasting serum lipid levels, possibly in relation to changes in insulin secretion.

Free fatty acid determination by peroxidase catalysed luminol chemiluminescence

A sensitive, specific, and partly automatic method for the analysis of free fatty acids is described. The assay involves activation of free fatty acids by acyl-CoA synthetase (EC 6.2.1.3) followed by oxidation of the thioesters by acyl-CoA oxidase. The H2O2 formed is determined in a reaction catalysed by horseradish peroxidase (EC 1.11.1.7) using luminol as electron donor. The assay has a linear range of 0.05 to 5 nmol of different free fatty acids (C10-C18) in the original sample. The efficiency of the method toward capric, lauric, myristic, palmitic, palmitoleic, stearic, oleic, and linoleic acid measured as recovery of light emission compared to that of H2O2 standards, was over 90%. AffiGel 501 was used to covalently bind the free thiol group in CoASH eliminating interference of this substance in the peroxidase-luminol reaction.

How does glibenclamide lower plasma glucose concentration in patients with type 2 diabetes?

Twelve patients with Type 2 diabetes and uncontrolled hyperglycaemia, never before treated with anti-diabetic drugs, were studied before and after several months of glibenclamide therapy. Fasting plasma glucose fell significantly (p less than 0.01) from 12.5 +/- 1.1 (mean +/- SE) to 8.3 +/- 0.4 mmol l-1 with glibenclamide therapy, as did glycosylated haemoglobin (from 12.0 +/- 0.9 to 8.4 +/- 0.7%). The improvement in blood glucose control was accompanied by an increase in postprandial plasma insulin concentration measured hourly from 0800 to 1600 h (p less than 0.001). Over the same period, plasma NEFA and lactate levels were significantly (p less than 0.001) lower after treatment with glibenclamide. Mean (+/- SE) insulin-mediated glucose metabolic clearance rate was evaluated during glucose clamp studies, and was significantly higher (p less than 0.001) after glibenclamide therapy at steady-state insulin levels of approximately 10 mU l-1 (53 +/- 3 vs 38 +/- 2 ml-2 min-1) and approximately 70 mU l-1 (78 +/- 9 vs 55 +/- 6 ml m-2 min-1). Hepatic glucose production was also lower following glibenclamide treatment at both the lower (56 +/- 5 vs 68 +/- 5 mg m-2 min-1) and higher 22 +/- 4 vs 32 +/- 6 mg m-2 min-1) insulin levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prazosin treatment on carbohydrate and lipoprotein metabolism in patients with hypertension

This study evaluated the effect of prazosin in controlled mild hypertension and evaluated select metabolic changes that occurred with prazosin monotherapy. Various aspects of glucose, insulin, and lipid metabolism were studied before and after approximately 10 weeks of prazosin treatment in 12 patients with mild hypertension. Prazosin was well tolerated and induced a significant decrease (p less than 0.001) in both systolic and diastolic blood pressures, without any change in body weight. Plasma concentrations of glucose, free fatty acid, and lactate, which were measured hourly from 8 A.M. to 4 P.M. following meals consumed at 8 A.M. and noon, did not change with prazosin treatment. However, the plasma insulin response from 8 A.M. to 4 P.M. decreased significantly (p less than 0.001) following prazosin treatment. In addition, fasting plasma triglyceride and cholesterol concentrations were significantly lower (p less than 0.05) in prazosin-treated persons, as were postprandial triglyceride concentrations (p less than 0.001). Lower total plasma triglyceride and cholesterol concentrations were accounted for by decreases in very low-density lipoprotein cholesterol and triglyceride and low-density lipoprotein cholesterol and triglyceride, whereas both high-density lipoprotein triglyceride and high-density lipoprotein cholesterol concentrations increased following prazosin treatment. Finally, although both apolipoprotein A1 and apolipoprotein B concentrations decreased in association with prazosin treatment, the decrease in apolipoprotein B was much greater in magnitude, leading to an increase in the ratio of apolipoprotein A1 to apolipoprotein B. In this study, treatment of mild hypertension with prazosin led to lower blood pressures and changes in insulin and lipoprotein metabolism that are important in this patient population.

Occurrence and possible roles of acetoacetyl-CoA thiolase and 3-ketoacyl-CoA thiolase in peroxisomes of an n-alkane-grown yeast, Candida tropicalis

Two kinds of 3-ketoacyl-CoA thiolases were found in the peroxisomes of Candida tropicalis cells grown on n-alkanes (C10-C13). One was a typical acetoacetyl-CoA thiolase specific only to acetoacetyl-CoA, while another was 3-ketoacyl-CoA thiolase showing high activities on the longer chain substrates. A high level of the latter thiolase activity in alkane-grown cells was similar to that of other enzymes constituting the fatty acid beta-oxidation system in yeast peroxisomes. These facts suggest that the complete degradation of fatty acids to acetyl-CoA is carried out in yeast peroxisomes by the cooperative contribution of acetoacetyl-CoA thiolase and 3-ketoacyl-CoA thiolase.