Acyl Transfer Rate Research Articles

Regiospecificity of Immobilized Candida antarctica Lipase B (CAL-B) towards 2,3-Diacyl-1-O-alkyl Glyceryl Ether in Ethanol.

Highly pure 2,3-dioleoyl-1-O-alkyl glyceryl ether (DOGE), whose 1-position is a lipase-tolerant ether bond, was chemically synthesized and its detailed regioselectivity and acyl transfer were confirmed. During ethanolysis using immobilized Candida antarctica lipase B (CAL-B) with DOGE as the substrate, monooleoyl-1-O-alkyl glyceryl ethers (MOGEs) and a few 1-alkyl glyceryl ethers were formed upon consumption of the substrate. The structure of MOGE was confirmed using nuclear magnetic resonance spectroscopy and only the isomer of 2-MOGE was formed, indicating that CAL-B has complete α- regiospecificity. During ethanolysis, 3-MOGE was formed via acyl migration. These results indicate that the formation of 1-alkyl glyceryl ethers is not due to the imperfect regiospecificity of CAL-B, but rather due to ethanolysis of the formed 3-MOGE. The ethanolysis rate at the 3-α-position of DOGE was faster and the rate of acyl transfer was slightly slower for chain lengths greater than 14. These results show for the first time that both deacylation at the 3-position and acyl migration from the 2- to 3-position are affected by the structure of 1-position.

Preparation of magnetic dialdehyde starch-immobilized phospholipase A1 and acyl transfer in reflection

In this paper, using a coprecipitation method to prepare Fe3O4 magnetic nanoparticles (Fe3O4 MNPS), magnetic dialdehyde starch nanoparticles with immobilized phospholipase A1 (MDSNIPLA) were successfully prepared by using green dialdehyde starch (DAS) instead of glutaraldehyde as the crosslinking agent. The Fe3O4 MNPS was characterized by infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), the Brunauer-Emmett-Teller (BET) surface area analysis method, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) et al. The results showed that the alkaline resistance and acid resistance of the enzyme were improved after the crosslinking of DAS. After repeated use (seven times), the relative activity of MDSNIPLA reached 56 %, and the magnetic dialdehyde starch nanoparticles (MDASN) had good carrier performance. MDSNIPLA was applied to enzymatic hydrolysis of phospholipids in the soybean oil degumming process. The results showed that the acyl transfer rate of sn-2-HPA was 14.01 %, and the content of free fatty acids was 1.144 g/100 g after 2 h reaction at 50 °C and pH 5.0 with appropriate boric acid. The immobilized enzyme has good thermal stability and storage stability, and its application of soybean oil improves the efficiency of the oil.

The influence of cholesterol on melittin lipidation in neutral membranes.

The effects of cholesterol on the process of intrinsic lipidation, whereby an acyl chain is transferred from a lipid as donor to a membrane-associated acceptor molecule, have been explored using melittin as the acceptor. Membranes comprising lipids with saturated acyl chains (1,2-dipalmitoyl sn-glycero-3-phosphocholine, DPPC; 1,2-dimyristoyl sn-glycero-3-phosphocholine, DMPC) yielded no acyl transfer, whereas membranes composed of lipids with unsaturated acyl chains (1,2-dioleoyl sn-glycero-3-phosphocholine, DOPC; 1-palmitoyl-2-oleoyl sn-glycero-3-phosphocholine, POPC) produced detectable lipidation activity. For all lipids, inclusion of cholesterol led to a significant increase in lipidation activity, with the greatest effect observed for 20 mol% cholesterol in POPC. In the case of membranes composed of POPC, the inclusion of cholesterol also produced small changes in the selectivity for transfer from the sn-1 vs. sn-2 positions of the lipid. Qualitatively, for fluid membranes, the trend in lipidation activity exhibits a positive correlation with the bending modulus of the bilayer and is accounted for in terms of the penetration depth of the peptide. Access of water to reactive intermediates also has the potential to influence lipidation rates.

Hybrid penicillin acylases with improved properties for synthesis of β-lactam antibiotics

Penicillin acylase (PA) from Escherichia coli can catalyze the acylation of 6-aminopenicillanic acid (6-APA), a conversion that is applicable in the biocatalytic preparation of semi-synthetic β-lactam antibiotics such as ampicillin. The efficiency of this kinetically controlled conversion, in which an amide or ester acts as the acyl donor, is dependent on the kinetic properties of the enzyme. To further improve the synthetic properties of PAs, family gene shuffling was performed with the PA-encoding genes of the PAs from E. coli, Kluyvera cryocrescens and Providencia rettgeri. Of these three PAs, the E. coli enzyme possessed the best properties for the synthesis of ampicillin. Shuffled recombinant libraries were pre-screened for activity by growth selection, followed by testing the catalytic performance in ampicillin synthesis using HPLC. Three clones with improved synthetic properties were selected and sequence analysis showed that the shuffled genes were hybrids of the PA-encoding genes from E. coli and K. cryocrescens, with additional point mutations. The hybrid enzymes displayed a 40–90% increase in the relative rate of acyl transfer to the β-lactam nucleus during ampicillin synthesis. This increase was not accompanied by a reduction of synthetic activity that has previously been reported for mutants of E. coli PA constructed by site-directed mutagenesis. Similar improvements in acyl transfer were obtained for the synthesis of amoxicillin, cephalexin and cefadroxil, making the new hybrid enzymes interesting candidates for the biocatalytic synthesis of several β-lactam antibiotics.

Changes in plasma phospholipids in the presence and absence of erythrocytes 31P-NMR time-course studies.

Whole human blood and plasma were incubated at 37 degrees C and 31P-NMR spectra were acquired from aliquots of plasma dissolved in sodium cholate. The narrow resonances of phospholipids were well resolved, allowing identification and accurate quantification of the various phospholipid classes. During the course of plasma incubation, the rate of increase in 2-lysphosphatidylcholine (2-LysoPtdCho) corresponded closely to the rate of decrease in phosphatidylcholine. However, little or no change was observed in the sphingomyelin concentrations. The rate of cholesteryl ester formation in plasma was also determined using HPLC and was observed to be similar to the rate of 2-LysoPtdCho increase in plasma; this is consistent with the rate of acyl transfer from phosphatidylcholine to free cholesterol catalysed by lecithin:cholesterol acyltransferase. However, during the course of whole blood incubation, the rate of 2-LysoPtdCho increase in plasma was significantly lower than the rate of 2-LysoPtdCho production during incubation of plasma alone (31 +/- 4 micromol x 1(-1) x h(-1) and 80 +/- 8 micromol x 1(-1) x h(-1), respectively). The difference between the rates can be attributed to the action of enzymes present in blood cells including those in the erythrocytes that catalyse acylation or hydrolysis of 2-LysoPtdCho.

Semi-empirical calculations of intramolecular acyl transfer in cis-enols of O-aroyl acetylacetones

Intramolecular acyl transfer was studied in eight aroyl derivatives of cis enols of acetylacetone using various semiempirical hamiltonians. The transition state geometry and activation energy for each derivative is reported. A reaction rate relative to that for the O-benzoyl derivative was calculated for each member in the series. The calculated relative rate constants were correlated to the substituent electronic constants, σ, and to experimental relative rate constants. Good correlations were obtained in both cases with the exceptions of the p-chloro and m-nitro aroyl groups. The rates of acyl transfer were enhanced by electron withdrawing aroyl groups. Calculations with the PM3 hamiltonians reproduced experimental trends better than using AM1.

A31P nuclear magnetic resonance investigation of acyl group transfer from phosphatidylcholine to yield lysophosphatidylcholine in human plasma

31P nuclear magnetic resonance (NMR) spectroscopy was used to measure the rate of acyl transfer from phosphatidylcholine (lecithin, PC) in whole plasma and in high density lipoprotein (HDL). Spectral deconvolution was used to resolve overlapping resonances in the 31P NMR spectra of the phospholipids. Mean values of the acyl group transfer rates from PC in plasma and HDL were 36 mumol L-1h-1 and 19 mumol L-1h-1, respectively. The reciprocal nature of the decrease in the spectral peak intensities of PC, compared to the increase in the intensities of the lysolecithin (lysoPC) peaks, suggested a substrate/product relationship consistent with the action of lecithin:cholesterol acyltransferase (LCAT), the enzyme responsible for the esterification of free cholesterol in plasma. LCAT involvement was confirmed by measuring the cholesterol esterification rate based on the 13C NMR spectra obtained on lipid extracts from plasma that had been incubated at 37 degrees C. Within experimental error, the rate of lysoPC formation in plasma was shown to be equal to that of cholesteryl ester formation.

Resolution of proline acylation problem for thiol capture strategy by use of a chloro-dibenzofuran template.

The acyl transfer rate for proline, in the prior thiol capture strategy, was enhanced by changing the electronic character of the dibenzofuran template. The rate of amide bond formation between proline and cysteine by the 1-chloro-4-hydroxy-6-mercaptodibenzofuran was measured to be 0.012 min-1, which translates to a half-life of 53 min. Further enhancement of the reaction rate was accomplished by the use of a 1,3-dichloro-dibenzofuran template. The k1 for the reaction was measured to be 0.093 min-1, and the half-life was calculated to be 7 min. To test the applicability of the activated template, 1-chloro-4-hydroxy-6-mercaptodibenzofuran, in peptide synthesis, the 34 amino acid long peptide, H-RPDFCLEPPYTGPCRKARNNFKSADECMRTCGGA-OH, was synthesized. This peptide represents the condensation of the N-terminal 13-mer and the C-terminal 21-mer of the basic pancreatic trypsin inhibitor.

Studies on the reaction mechanism of a microbial lipase/acyltransferase using chemical modification and site-directed mutagenesis.

Aeromonas hydrophila releases a protein which is a member of the lipase superfamily, similar in reaction mechanism to the important mammalian plasma enzyme lecithin-cholesterol acyltransferase. We have used chemical modification and site-directed mutagenesis of the protein to identify amino acids which may be involved in catalysis. The enzyme was unaffected by phenylmethylsulfonyl fluoride, but it was almost completely inhibited by another serine-reactive compound, diethyl p-nitrophenyl phosphate. A serine selectively modified by this reagent was identified by sequencing the amino-terminal region of the protein. It was located at position 16, in the short consensus sequence shared by the enzyme with other lipases. When this serine was changed to asparagine the product was an enzymatically inert protein which nevertheless retained the surface activity of the wild-type enzyme, suggesting its ability to bind to substrate was not changed. Diethylpyrocarbonate treatment drastically reduced the rate of acyl transfer by the native enzyme, but this did not appear to be due to modification of an essential histidine, since inhibition was not reversed by addition of hydroxylamine. We have shown that only two of the histidines in the enzyme can be involved in catalysis (Hilton, S., McCubbin, W. D., Kay, C.M., and Buckley, J. T. (1990) Biochemistry, 29, 9072-9078). Replacing both of these with asparagines had little or no effect on enzyme activity. These results indicate that, in apparent contrast to other lipases, histidine does not participate in the reaction catalyzed by the microbial enzyme. Since catalysis was not inhibited by sulfhydryl reagents, we conclude that a free cysteine is also not required for activity. This may distinguish the microbial enzyme from the mammalian acyltransferase.

2-Acylglycerolphosphoethanolamine acyltransferase/acyl-acyl carrier protein synthetase is a membrane-associated acyl carrier protein binding protein

Two enzymatic activities, 2-acylglycerolphosphoethanolamine (2-acyl-GPE) acyltransferase and acyl-acyl carrier protein (acyl-ACP) synthetase, were solubilized and purified from Escherichia coli membranes. Electrophoretic analysis of the final product of the purification procedure revealed a single protein species with an apparent molecular mass of 27 kilodaltons. The ratio of acyltransferase to synthetase activities remained the same throughout the purification scheme indicating that both activities were catalyzed by the same enzyme. 2-Acyl-GPE acyltransferase exhibited an apparent ACP Km of 64 nM under standard assay conditions that increased to 10 microM when the assay was conducted in the presence of 0.4 M LiCl. Acyl-ACP synthetase activity was not detected in the absence of 0.4 M LiCl, and the apparent ACP Km for this reaction was 16 microM. Direct evidence that ACP was a subunit of the acyltransferase/synthetase was obtained by the adsorption of both catalytic activities to an ACP-Sepharose affinity column and by the binding of [3H]ACP to the purified enzyme preparation. The apparent Km for acyl-ACP was 13 microM, and the rate of acyl transfer from this acyl donor was enhanced by the addition of 0.4 M LiCl indicating that the exchange of enzyme-bound ACP for acyl-ACP was a determinant factor in the rate of phosphatidylethanolamine formation from acyl-ACP. These data indicate that the 2-acyl-GPE acyltransferase and acyl-ACP synthetase reactions are catalyzed by the same membrane protein that possesses a high affinity binding site for soluble ACP.

Plasma cholesterol esterification rate in hyperlipoproteinaemia: relation to cholesterol elimination.

The present study was undertaken to determine the relationship between plasma lecithin: cholesterol acyl transfer (LCAT) rate and cholesterol and bile acid turnover in hyperlipidaemia. Nineteen healthy controls, 19 patients with hyperlipoproteinaemia (HLP) type IIa and 12 patients with HLP type IV were studied under standardized dietary conditions. Bile acid kinetics was determined with the aid of [14C]labelled cholic acid and chenodeoxycholic acid. In the hyperlipidaemic patients, cholesterol balance was calculated as the sum of bile acid synthesis plus daily faecal excretion of neutral C27 steroids minus dietary intake of cholesterol. The plasma LCAT rate was determined simultaneously. The mean values of bile acid formation, cholesterol balance, and LCAT rate in HLP type IV patients exceeded those in HLP type IIa patients or in the controls. An increased plasma LCAT rate was found among HLP type IV patients with and without evidence of cardiovascular disease. Plasma LCAT rate correlated positively with bile acid formation (Rs = +0.78, p less than 0.01) and cholesterol balance (Rs = +0.88, p less than 0.002) in HLP type IV. No such relationships were obtained in the controls or in HLP type IIa. It is suggested that an increased production and/or flux of VLDL in HLP type IV is linked to an enhanced plasma LCAT rate and to an increased formation and metabolism of cholesterol in the liver.

Plasma cholesterol esterification rate in hyperlipoproteinaemia: Relation to cholesterol elimination

The present study was undertaken to determine the relationship between plasma lecithin: cholesterol acyl transfer (LCAT) rate and cholesterol and bile acid turnover in hyperlipidaemia. Nineteen healthy controls, 19 patients with hyperlipoproteinaemia (HLP) type IIa and 12 patients with HLP type IV were studied under standardized dietary conditions. Bile acid kinetics was determined with the aid of [14C]labelled cholic acid and chenodeoxycholic acid. In the hyperlipidaemic patients, cholesterol balance was calculated as the sum of bile acid synthesis plus daily faecal excretion of neutral C27 steroids minus dietary intake of cholesterol. The plasma LCAT rate was determined simultaneously. The mean values of bile acid formation, cholesterol balance, and LCAT rate in HLP type IV patients exceeded those in HLP type IIa patients or in the controls. An increased plasma LCAT rate was found among HLP type IV patients with and without evidence of cardiovascular disease. Plasma LCAT rate correlated positively with bile acid formation (Rs = +0.78, p<0.01) and cholesterol balance (Rs = +0.88, p<0.002) in HLP type IV. No such relationships were obtained in the controls or in HLP type IIa. It is suggested that an increased production and/or flux of VLDL in HLP type IV is linked to an enhanced plasma LCAT rate and to an increased formation and metabolism of cholesterol in the liver.

Fatty acid metabolism by a particulate fraction from germinating peas

The incorporation of fatty acids into lipid fractions was studied using a high-speed particulate fraction from germinating peas ( Pisum sativum cv Feltham First). The acids were incorporated principally into the acyl-CoA and polar lipid fractions, with unsaturated fatty acids labelling the latter fraction at higher rates than saturated substrates. α-Hydroxylation also occurred. Oleate from oleoyl-CoA or oleoyl-acyl carrier protein was incorporated into polar lipids faster than from ammonium oleate. The incorporation of fatty acids into polar lipids was dependent on the presence of CoA and ATP in the medium and on the consequent generation of acyl-CoA's. Time-course studies and experiments when two fatty acid substrates were added consecutively confirmed the role of acyl-CoA's in the transfer of acyl groups to phospholipids. Although CoA was necessary when acyl-CoA's had to be generated, high concentrations were found to inhibit the rate ofacyl transfer. The results are discussed in terms ofthe ‘witching mechanism’ for controlling the fate of fatty acids in the plant cell.

Lecithin: Cholesterol acyl transfer rate and high density lipoprotein level in coronary artery disease

The lecithin:cholesterol acyl transfer (LCAT) reaction occurs in connection with the high density lipoproteins (HDL) and might have importance for the development of atheromatosis. The LCAT rate and the lipoprotein concentrations in plasma were therefore determined in 82 patients, 40–60 years old, with incapacitating angina pectoris and significant lesions at coronary angiography. Thirty-eight cases were normolipidemic and 22 had type IV hyperlipidemia while the others had different types of hypercholesterolemia (n = 7) or were pharmacologically treated for previously diagnosed hyperlipidemia (n = 11) or diabetes mellitus. The normolipidemic group and the type IV group with coronary artery disease were separately compared to one normolipidemic (n = 44) and one type IV hyperlipidemic (n = 29) control group of healthy subjects of about the same age. The fractional LCAT rate (% · h −1) was lower in patients compared to controls both regarding the normolipidemic and type IV subjects. The molar LCAT rate (μmol · 1 −1 · h −1) did not differ between normolipidemic cases and controls while it was lower in type IV patients with coronary artery disease than in the type IV controls. The HDL total cholesterol (TC) concentration and the HDL-TC/TC ratio were lower in normolipidemic cases than in normolipidemic controls while both cases and controls with type IV hyperlipidemia showed equally low levels of these parameters. In conclusion, both a reduced fractional LCAT rate and a decreased HDL-TC/TC ratio might be indicators of disturbances of the cholesterol ester metabolism and might contribute to the development of coronary atheromatosis.

Lecithin: cholesterol acyl transfer rate in hypothyroidism and hyperthyroidism.

The initial rate of lecithin: cholesterol acyl transferase and serum concentration of lipids were determined in euthyroid, hypothyroid and hyperthyroid subjects. In hyperthyroid subjects, the serum levels of total and free cholesterol were significantly lower than in normal subjects and the fractional lecithin: cholesterol acyl transfer rate was significantly higher than in normal subjects. The molar lecithin: cholesterol acyl transfer rate was also higher than in normal subjects, but not significantly. The free cholesterol/total cholesterol ratio in hypothyroid females and the serum levels of triglyceride and free fatty acid in hypothyroid male were significantly higher than in normal subjects. The fractional lecithin: cholesterol acyl transfer rates in hypothyroid females were significantly lower than in normal females. After treatment of the thyroid disease the fractional and molar lecithin: cholestorol cholesterol acyl transfer rate approached the normal values. There was a positive correlation between fractional and molar lecithin: cholesterol acyl transfer rate and thyroxine. These results suggest that thyroid hormone influences the cholesterol esterification through the activation of lecithin: cholesterol acyltransferase.

Acyl substituent effects on rates of acyl transfer to thiolate, hydroxide, and oxy dianions

Acyl substituent effects on rates of acyl transfer to thiolate, hydroxide, and oxy dianions

Lecithin: cholesterol acyl transfer rate and high density lipoproteins in plasma during dietary and cholestyramine treatment of type Ila hyperlipoproteinaemia

Abstract. Changes in the lecithin:cholesterol acyl transfer rate and the concentrations of lipids and high density lipoprotein lipids in plasma were studied during dietary and cholestyramine treatment of type IIa subjects. Samples were obtained from twenty subjects before and 2 months after the start of a cholesterol lowering diet. Sixteen subjects were studied 1 month after the addition of cholestyramine treatment to the dietary regimen.During 2 months of dietary modification the mean concentrations of cholesterol, phospholipids and low density lipoprotein cholesterol were reduced by 10%. In the high density lipoprotein fraction there was a 10% mean increase of the cholesterol but no change of the mean phospholipid concentration. There were no changes of the mean triglyceride concentration or the mean fractional or molar lecithin:cholesterol acyl transfer rates in plasma.One month after the addition of cholestyramine to the diet there were further reductions in the mean plasma concentrations of cholesterol by 22.5%, phospholipids by 12% and low density lipoprotein cholesterol by 32%. The mean triglyceride concentration and the mean concentration and composition of the high density lipoprotein fraction were unchanged. The mean fractional Iecithin :cholesterol acyl transfer rate was increased by 30%. The type IIa subjects with high molar lecithin: cholesterol acyl transfer rates during the diet showed increments of molar lecithin:cholesterol acyl transfer rates during cholestyramine therapy.Interpretations of these findings in relation to lipoprotein metabolism are discussed.

Lecithin: Cholesterol acyl transfer rate and high density lipoproteins in plasma during dietary and clofibrate treatment of hypertriglyceridemic subjects

Effects of lipid-lowering treatment on the lecithin: cholesterol acyl transfer (LCAT) rate and the concentrations of lipids and high density lipoproteins (HDL) lipids in plasma were determined in hypertriglyceridemic subjects. Thirty-nine subjects were studied before and after two months on a weight reducing diet. Twenty subjects were studied also one month after the addition of clofibrate to the dietary regimen. After two months on the diet the mean body weight had decreased by 4.5%. There were reductions in the mean plasma concentrations of triglycerides (TG) by 18% and in total cholesterol (TC), unesterified cholesterol (UC) and phospholipids (PL) by 12%. The mean HDL-TC concentrations increased by 10%, while the mean HDL-PL concentration was unchanged. During two months of diet the mean molar LCAT rate decreased by 17% and the mean fractional LCAT rate was reduced by 6%. One month after the addition of clofibrate there were reductions in the mean plasma concentrations of TG by 43% and of TC, UC and PL by 15%. The mean HDL-TC concentration increased by 22%, while the mean HDL-PL concentration was enhanced by 9%. The mean molar LCAT rate decreased by 10%, based on reductions in the type IV subjects with high molar LCAT rates before the clofibrate treatment. The mean fractional LCAT rate was not changed in the type IV subjects but increased in the type IIb and type III subjects during clofibrate therapy. The changes in the molar LCAT rate correlated positively with the changes in the body mass after two months on the diet and with the changes in the concentrations of TG, UC and PL in plasma obtained with both kinds of treatment. The changes in the fractional LCAT rate were negatively correlated with the changes of low density lipoprotein-TC concentrations during both kinds of treatment.

Changes of Plasma Lipid Metabolism in Males during Estrogen Treatment for Prostatic Carcinoma*

Fourteen patients with prostatic carcinoma were treated with 1.0-0.5 mg ethinyl estradiol orally daily and 160-80 mg polyestradiol phosphate im monthly. Lipid concentrations were determined in plasma and the high density lipoprotein fraction, and the plasma lecithin-cholesterol acyl transfer rate was measured before and 1 and 6 months after the start of therapy. During treatment, the concentration of total cholesterol was unchanged while there was a 60% increase of high density lipoprotein-total cholesterol. Triglyceride (TG) concentration increased 40%, indicating an augmented level of very low density lipoprotein concentration. The plasma lecithin-cholesterol acyl transfer rate increase 20-35%, indicating that an increased rate of production and turnover of TG, cholesteryl esters, and very low density lipoproteins probably was a main cause of the elevated TG concentration. The potential effects on the development of atherosclerosis by the plasma lipid changes during estrogen treatment are discussed.

Lecithin: Cholesterol Acyl Transfer Rate in Plasma and its Relations to Lipoprotein Concentrations and to Kinetics of Bile Acids and Triglycerides in Hyperlipoproteinemic Subjects

The lecithin:cholesterol acyl transfer (LCAT) rate and the concentrations of lipids and lipoproteins in plasma were determined in 85 normolipidemic reference subjects and in 89 subjects with different types of hyperlipoproteinemia (38 type 11a, 9 type lib. 2 type III. 38 type IV and 2 type V). The mean molar LCAT rate was lower in the reference group than in all types of hyperlipoproteinemia. The type IV and type V subjects had the highest molar LCAT rates. The mean fractional LCAT rate was reduced in type Ha and elevated in type IV compared to the reference group. In the hyperlipoproteinemic subjects the molar LCAT rate correlated positively with the triglyceride (TG)or the very low density lipoprotein (VLDL) concentration in plasma and with the body weight. The fractional LC AT rate correlated negatively with the LDL-total cholesterol (TC) concentration in plasma. After two months on a weight-reducing diet the mean molar and fractional LCAT rates were reduced by 17% and 6% respectively in 39 hypertriglyceridemic subjects. The changes of the molar LCAT rate correlated positively with the changes of the TG. unesterified cholesterol, and phospholipid concentrations in plasma and with the changes of the body weight. The changes of the fractional LCAT rate correlated negatively with the changes of the LDL-TC concentration in plasma. The production rate of bile acids and the turnover of endogenous TG, which were determined in 7 type IV subjects, correlated positively with the molar LCAT rate. There was no correlation between the bile acid production and the molar LCAT rate in 12 type Ila subjects. The results indicate that there are close relations between the production rate of cholesteryl esters (CE)in plasma and the production rate of VLDL and bile acids in type IV subjects. It is suggested that the molar LCAT rate determined in vitro might reflect the turnover of CE in plasma in vivo.