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At least 19 recordsLinked to original sources
PubMed1975

Partial purification, properties, and subcellulsr distribution of rat liver phosphatidate phosphatase.

Phosphatidate phosphatase (EC 3.1.3.4Y was purified 15- to 20-fold from the soluble fraction of rat liver. The purification procedure involved calcium phosphate gel adsorption and elution, ammonium sulfact precipitation, and molecular-sieve chromatography. For the enzyme assay, and aqueous dispersion of phosphatidate, rather than "membrane-bound" phosphatidate, was used as substrate. The partially purified enzyme depends almost entirely on the presence of Mg2+ for its activity. Morover, the activity of the enzyme is stimulated by phosphatidylcholine. The enzyme exhibits a high substrate specificity for phosphatidate. The apparent Km for phosphatidate is approximately 0.05 mM. The optimum pH is between 7.4 and 7.6. The enzyme is inhibited by fluoride and by p-chloromercuribenzoate. The subcellular distribution of phosphatidate phosphatase in rat liver was studied by assaying the activity of the enzyme in the presence of Mg2+ and phosphatidylcholine. In contrast ot the results of previous studies, most of the enzyme activity was found in the soluble fraction.

Adsorption↗
PubMed1996

Phosphatidate phosphatases of mammals, yeast, and higher plants.

Phosphatidate phosphatase (EC 3.1.3.4) catalyzes the hydrolysis of phosphatidate to yield sn-1,2-diacylglycerol and inorganic phosphate. In mammalian systems, forms of phosphatidate phosphatase involved in glycerolipid synthesis and signal transduction have been identified. Forms of the enzyme involved in signal transduction have been purified and partially characterized. In yeast, phosphatidate phosphatases associated with the endoplasmic reticulum and mitochondria have also been purified and partially characterized. Information on phosphatidate phosphatases from mammals and yeast is useful in characterizing the enzyme from plant systems. This review examines progress on the characterization of phosphatidate phosphatases from mammals, yeast, and higher plants. The purification and characterization of the phosphatidate phosphatase involved in glycerolipid synthesis in developing oilseeds may lead to the identification of the encoding gene. Increasing our understanding of the enzymes of lipid synthesis in developing seeds will aid in the development of biotechnological strategies for seed oil modification.

Animals↗
PubMed1997

Phosphatidate phosphatases and diacylglycerol pyrophosphate phosphatases in Saccharomyces cerevisiae and Escherichia coli.

Phosphatidate phosphatase plays a major role in the synthesis of phospholipids and triacylglycerols in the yeast Saccharomyces cerevisiae. Membrane- and cytosolic-associated forms of the enzyme have been isolated and characterized. These enzymes are Mg2+-dependent and N-ethylmaleimide-sensitive. The expression of a membrane-associated form of phosphatidate phosphatase is regulated by growth phase and inositol supplementation, whereas enzyme activity is regulated by lipids, nucleotides, and by phosphorylation. Phosphatidate phosphatase is coordinately regulated with other phospholipid biosynthetic enzymes including phosphatidylserine synthase. Diacylglycerol pyrophosphate phosphatase is a novel enzyme of phospholipid metabolism which is present in S. cerevisiae, Escherichia coli, and mammalian cells. This enzyme possesses a phosphatidate phosphatase activity which is Mg2+-independent and N-ethylmaleimide-insensitive and is distinct from the Mg2+-dependent and N-ethylmaleimide-sensitive form of phosphatidate phosphatase. Genes encoding for diacylglycerol pyrophosphate phosphatase have been isolated from S. cerevisiae and E. coli. The deduced protein sequences of these genes show homology to the sequence of the mouse PAP2 (Mg2+-independent and N-ethylmaleimide-insensitive phosphatidate phosphatase) protein, especially in a novel phosphatase sequence motif. Rat liver PAP2 displays diacylglycerol pyrophosphate phosphatase activity.

Amino Acid Sequence↗
PubMed1988

Regulation of phosphatidate phosphatase activity by inositol in Saccharomyces cerevisiae.

Regulation of phosphatidate phosphatase (EC 3.1.34) activity was examined in Saccharomyces cerevisiae cells supplemented with phospholipid precursors. Addition of inositol to the growth medium of wild-type cells resulted in a twofold increase in phosphatidate phosphatase activity. The increase in phosphatidate phosphatase activity was not due to soluble effector molecules, and inositol did not have a direct effect on enzyme activity. The phosphatidate phosphatase activity associated with the mitochondrial, microsomal, and cytosolic fractions of the cell was regulated by inositol in the same manner. Cells supplemented with inositol had elevated phospholipid levels and reduced triacylglycerol levels compared with unsupplemented cells. Serine, ethanolamine, and choline did not significantly affect the phosphatidate phosphatase activity of cells grown in the absence or presence of inositol. Enzyme activity was not regulated in inositol biosynthesis regulatory mutants, suggesting that regulation by inositol is coupled to regulation of inositol biosynthesis. Phosphatidate phosphatase activity was pleiotropically expressed in structural gene mutants defective in phospholipid biosynthesis. These results suggested that phosphatidate phosphatase was regulated by inositol at a genetic level.

Culture Media↗
PubMed1973

Glycerolipid synthesis in rat adipose tissue. II. Properties and distribution of phosphatidate phosphatase.

The properties and subcellular distribution of phosphatidate phosphatase (EC 3.1.3.4) from adipose tissue have been investigated. The enzyme was assayed using both aqueous phosphatidate and membrane-bound phosphatidate as substrates. When measured with aqueous substrate, activity was detected in the mitochondria, the microsomes, and the soluble fraction. Mg(2+) at low concentration stimulated the phosphatidate phosphatase from soluble and microsomal fractions but had no effect on the mitochondrial phosphatidate phosphatase. At higher concentration Mg(2+) was inhibitory. In the presence of Mg(2+), the phosphatidate phosphatase from soluble and microsomal fractions was active against membrane-bound phosphatidate. No activity was demonstrated with membrane-bound substrate in the absence of Mg(2+). Mitochondria did not contain activity toward the membrane-bound substrate. The rate of utilization of aqueous phosphatidate was always higher than that of membrane-bound substrate. These results indicate that there are at least two different phosphatidate phosphatases in adipose tissue.

Adipose Tissue↗
PubMed1977

Soluble rat adipocyte phosphatidate phosphatase activity: characterization and effects of fasting and various lipids.

Phosphatidate phosphatase (phosphatidate phosphohydrolase, EC 3.1.3.4) was present at very high specific activity in the soluble fraction of isolated rat adipocytes. Using phosphatidate in aqueous dispersion 90% of its hydrolysis depended on the presence of Mg2+. Mg2+ appeared to almost saturate the enzyme at 20-40 mM with no indication of an optimum. The substrate concentration was optimum at 1.2 mM and the pH at 6.8. Initial rates were linear for only 4-5 min at optimum conditions. Increasing inhibition occurred at high phosphatidate concentrations. At optimum conditions acid or alkaline phosphatase activity was not measurable. The Mg2+-dependent activity was enhanced by 3-sn-phophatidylcholine and inhibited by albumin, 3-sn-phosphatidyletanolamine, 3-sn-phosphatidylinositol, diacylglycerol, oleoyl-CoA, and oleate. Oleoyl-CoA was the most potent "effector". Fasting for 24, 48 and 72 h decreased the activity both relative to protein and to DNA. The activity thus decreased to about one-third of that of the fed rat during 72 h of fasting. The effects of Mg2+, various lipids, and fasting may indicate that some form of control of glyceride synthesis can be exerted through the soluble phosphatidate phosphatase.

Adipose Tissue↗
PubMed1996

Regulation of phosphatidate phosphatase activity from the yeast Saccharomyces cerevisiae by phospholipids.

Regulation of Saccharomyces cerevisiae membrane-associated phosphatidate phosphatase (3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4) activity by phospholipids was examined using purified enzyme and Triton X-100/phospholipid-mixed micelles. Anionic phospholipids activated phosphatidate phosphatase activity whereas zwitterionic phospholipids had a slight inhibitory effect on activity. Cardiolipin (A0.5 = 1.9 mol %), CDP-diacylglycerol (A0.5 = 2.6 mol %), and phosphatidylinositol (A0.5 = 5.5 mol %) were the most potent anionic phospholipid activators. Enzyme activation by cardiolipin (n=2.8), CDP-diacylglycerol (n=2.1), and phosphatidylinositol (n=3.3) followed positive cooperative kinetics. A kinetic analysis was performed to determine the mechanism of phosphatidate phosphatase activation by anionic phospholipids. The dependence of phosphatidate phosphatase on phosphatidate was cooperative (n approximately 2.2) in the absence and presence of phospholipid activators. Cardiolipin, CDP-diacylglycerol, and phosphatidylinositol were mixed competitive activators of phosphatidate phosphatase activity. The major effect of the activators was to cause a decrease in the Km for phosphatidate. Sphinganine, a positively charged sphingoid base, inhibited phosphatidate phosphatase activity and antagonized the activation of the enzyme by cardiolipin and phosphatidylinositol. Sphinganine caused an increase in the cooperativity of cardiolipin activation, but had little effect on the A0.5 value for cardiolipin. On the other hand, sphinganine had little effect on the cooperativity of phosphatidylinositol activation, but caused an increase in the A0.5 value for phosphatidylinositol. The activation constants for cardiolipin, CDP-diacylglycerol, and phosphatidylinositol were within the range of their cellular concentrations. These results suggested that the activation of phosphatidate phosphatase activity by anionic phospholipids may be physiologically relevant.

Cardiolipins↗
PubMed1993

Regulation of phosphatidate phosphatase activity from the yeast Saccharomyces cerevisiae by sphingoid bases.

The regulation of Saccharomyces cerevisiae membrane-associated phosphatidate phosphatase (3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4) activity by sphingoid bases was examined using Triton X-100/lipid-mixed micelles. Sphingosine, phytosphingosine, and sphinganine inhibited purified preparations of the 104- and 45-kDa forms of phosphatidate phosphatase in a dose-dependent manner. The structural requirements for the sphingoid base inhibition of phosphatidate phosphatase activity were a free amino group and a long chain hydrocarbon. A detailed kinetic analysis was performed to determine the mechanism of phosphatidate phosphatase inhibition by sphingoid bases. The phosphatidate phosphatase dependence on phosphatidate was cooperative (Hill numbers of approximately 2) in the absence and presence of sphingoid bases. Sphingosine, phytosphingosine, and sphinganine were parabolic competitive inhibitors of phosphatidate phosphatase activity. This indicated that more than one inhibitor molecule contributed to the exclusion of phosphatidate from the enzyme. The aKi values (inhibitor constants) for sphingosine, phytosphingosine, and sphinganine were 1.5, 0.4, and 0.2 mol %, respectively, and the Km value for phosphatidate was 2.2 mol %. The cellular concentrations of free phytosphingosine and sphinganine were 0.16 and 0.53 mol %, respectively, relative to the total phospholipids in S. cerevisiae. The cellular concentrations of phytosphingosine and sphinganine were in the range of the aKi values for these sphingoid bases. These results raised the suggestion that phosphatidate phosphatase activity may be regulated in vivo by sphingoid bases.

Amines↗
PubMed1994

Regulation of phosphatidate phosphatase activity from the yeast Saccharomyces cerevisiae by nucleotides.

Regulation of Saccharomyces cerevisiae membrane-associated phosphatidate phosphatase (3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4) activity by nucleotides was examined using pure enzyme and Triton X-100/phosphatidate-mixed micelles. Adenosine, guanosine, cytidine, and uridine nucleotides inhibited phosphatidate phosphatase activity in a dose-dependent manner. ATP and CTP were the most potent inhibitors of the enzyme. A kinetic analysis was performed to determine the mechanism of enzyme inhibition by nucleotides. The mechanism of inhibition by ATP and CTP with respect to phosphatidate (the substrate) was complex. The dependence of phosphatidate phosphatase activity on phosphatidate was cooperative, and nucleotides affected both Vmax and Km. ATP did not inhibit phosphatidate phosphatase activity by binding to the enzyme or to phosphatidate. Phosphatidate phosphatase dependence on Mg2+ ions (the cofactor) followed saturation kinetics, and the mechanism of nucleotide inhibition with respect to Mg2+ ions was competitive. Thus, the mechanism of enzyme inhibition by nucleotides was the chelation of Mg2+ ions. The inhibitor constant for ATP was lower than its cellular concentration in glucose-grown cells. However, the inhibitor constant for ATP was higher than its cellular concentration in glucose-starved cells. Changes in the cellular concentration of ATP affected the proportional synthesis of triacylglycerols and phospholipids. These results were consistent with the regulation of phosphatidate phosphatase activity by ATP through a Mg2+ ion chelation mechanism.

Binding Sites↗
PubMed1989

Purification and characterization of phosphatidate phosphatase from Saccharomyces cerevisiae.

Membrane-associated phosphatidate phosphatase (EC 3.1.3.4) was purified 9833-fold from the yeast Saccharomyces cerevisiae. The purification procedure included sodium cholate solubilization of total membranes followed by chromatography with DE53, Affi-Gel Blue, hydroxylapatite, Mono Q, and Superose 12. The procedure resulted in the isolation of a protein with a subunit molecular weight of 91,000 that was apparently homogeneous as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Phosphatidate phosphatase activity was associated with the purified 91,000 subunit. The molecular weight of the native enzyme was estimated to be 93,000 by gel filtration chromatography with Superose 12. Maximum phosphatidate phosphatase activity was dependent on magnesium ions and Triton X-100 at pH 7. The Km value for phosphatidate was 50 microM, and the Vmax was 30 mumol/min/mg. The turnover number (molecular activity) for the enzyme was 2.7 x 10(3) min-1 at pH 7 and 30 degrees C. The activation energy for the reaction was 11.9 kcal/mol, and the enzyme was labile above 30 degrees C. Phosphatidate phosphatase activity was sensitive to thioreactive agents. Activity was inhibited by the phospholipid intermediate CDP-diacylglycerol and the neutral lipids diacylglycerol and triacylglycerol.

Cholic Acid↗
PubMed1992

The 45- and 104-kDa forms of phosphatidate phosphatase from Saccharomyces cerevisiae are regulated differentially by phosphorylation via cAMP-dependent protein kinase.

Evidence is presented that demonstrated that the 45- and 104-kDa forms of phosphatidate phosphatase from Saccharomyces cerevisiae (Morlock, K. R., McLaughlin, J. J., Lin, Y.-P., and Carman, G. M. (1991) J. Biol. Chem. 266, 3586-3593) were regulated differentially by phosphorylation. Purified 45-kDa phosphatidate phosphatase was phosphorylated by cAMP-dependent protein kinase whereas purified 104-kDa phosphatidate phosphatase was not phosphorylated. cAMP-dependent protein kinase catalyzed the phosphorylation of pure 45-kDa phosphatidate phosphatase at a serine residue which resulted in a stimulation (2.4-fold) of phosphatidate phosphatase activity. Alkaline phosphatase catalyzed the dephosphorylation of pure 45-kDa phosphatidate phosphatase which resulted in an inhibition (1.3-fold) of phosphatidate phosphatase activity. Results of studies using mutants (bcy1 and cyr1) defective in cAMP-dependent protein kinase activity corroborated the results of the phosphorylation studies using pure preparations of phosphatidate phosphatase. The 45-kDa phosphatidate phosphatase phosphorylated in vitro and in vivo had phosphopeptides in common. The activation of the GAL10-RAS2val19 allele in mutant cells resulted in an increase in the synthesis of diacylglycerols and triacylglycerols. These results were consistent with the phosphorylation and activation of 45-kDa phosphatidate phosphatase by cAMP-dependent protein kinase in vivo.

Alleles↗
PubMed1987

Role of acetaldehyde in ethanol-induced increase in the activity of phosphatidate phosphatase in rat liver.

The effect of ethanol on the activity of phosphatidate phosphatase was studied in rat liver using membrane-bound phosphatidate and phosphatidate emulsion as substrate. A single large dose of ethanol (5 g/kg body wt) caused an increase in the enzyme activity measured with membrane-bound phosphatidate after an approximate 2-hr lag period in both cytosolic and microsomal fraction and the increase was approximately 2.2- and 1.8-fold that in control rats at 5 hr in cytosol and microsomes, respectively. A similar time-course of the increase was obtained with phosphatidate emulsion as substrate. These ethanol-induced increases in the activity of cytosolic and microsomal phosphatidate phosphatase were blocked by the pretreatment of rats with actinomycin D. The ethanol-induced rise in the activity of cytosolic and microsomal phosphatidate phosphatase measured with membrane-bound phosphatidate was abolished when rats were injected with pyrazole prior to ethanol administration. On the other hand, pretreatment with cyanamide enhanced the increase in cytosolic activity produced by a suboptimal dose of ethanol (1 g/kg), while microsomal activity was not affected by the same treatment, suggesting that acetaldehyde may be selectively involved in the ethanol-induced increase in the activity of cytosolic phosphatidate phosphatase. This hypothesis was supported by a finding that administration of paraldehyde, a cyclic trimer of acetaldehyde, produced an increase (35%) in cytosolic activity, but not in microsomal activity.

Acetaldehyde↗
PubMed2006

Roles of phosphatidate phosphatase enzymes in lipid metabolism.

Phosphatidate phosphatase (PAP) enzymes catalyze the dephosphorylation of phosphatidate, yielding diacylglycerol and inorganic phosphate. In eukaryotic cells, PAP activity has a central role in the synthesis of phospholipids and triacylglycerol through its product diacylglycerol, and it also generates and/or degrades lipid-signaling molecules that are related to phosphatidate. There are two types of PAP enzyme, Mg(2+) dependent (PAP1) and Mg(2+) independent (PAP2), but only genes encoding PAP2 enzymes had been identified until recently, when a gene (PAH1) encoding a PAP1 enzyme was found in Saccharomyces cerevisiae. This discovery has revealed a molecular function of the mammalian protein lipin, a deficiency of which causes lipodystrophy in mice. With molecular information now available for both types of PAP, the specific roles of these enzymes in lipid metabolism are being clarified.

Animals↗
PubMed1992

Feedback inhibition of phosphatidate phosphatase from spinach chloroplast envelope membranes by diacylglycerol.

Because the envelope phosphatidate phosphatase plays a pivotal role in chloroplast glycerolipid metabolism, we have analyzed whether diacylglycerol could be a regulatory factor of the enzyme. Using isolated envelope membranes in which the level of diacylglycerol was modified by thermolysin treatment of intact chloroplasts to destroy the galactolipid:galactolipid galactosyltransferase, we have demonstrated that phosphatidate phosphatase activity was reduced when the membrane was enriched in diacylglycerol. All 1,2-diacylglycerol molecular species assayed were demonstrated to inhibit the enzyme to about the same extent. Kinetic studies with envelope from thermolysin-treated chloroplasts were performed in the absence and presence of diacylglycerol, and diacylglycerol was shown to be a powerful competitive inhibitor of the reaction. Finally, using isolated intact spinach chloroplasts, we have demonstrated that in situ phosphatidate phosphatase activity can be modulated by the level of diacylglycerol present in the membrane. The relevance of phosphatidate phosphatase inhibition by diacylglycerol in the regulation of chloroplast glycerolipid biosynthesis is discussed.

Cell Fractionation↗
PubMed1989

Microsomal phosphatidate phosphatase in maturing safflower seeds.

An assay system comprising sodium phosphatidate, phosphatidylcholine, and bovine serum albumin has been developed for the reproducible determination of phosphatidate phosphatase activity in maturing seeds of safflower (Carthamus tinctorius L.). The activity was detected in both membrane and soluble fractions, and the microsomal phosphatidate phosphatase was characterized. The optimum pH for Pi release was 6.7, and the activity depended on the concentration of Mg(2+). Phosphatidylcholine and bovine serum albumin stimulated the phosphatase reaction. This phosphatase was highly specific for phosphatidate; lysophosphatidate, and water-soluble phosphate esters did not serve as substrate. The specific activity was approximately 20 nanomoles per minute per milligram of protein, which was close to that of glycerol-phosphate acyltransferase and higher than that of diacylglycerol acyltransferase. Furthermore, the activity per seed was enough to account for the rate of triacylglycerol accumulation in vivo. The step of diacylglycerol formation by phosphatidate phosphatase does not appear to be rate-limiting for triacylglycerol synthesis during seed maturation.

Journal Article↗
PubMed1990

Intracellular translocation of phosphatidate phosphatase in maturing safflower seeds: a possible mechanism of feedforward control of triacylglycerol synthesis by fatty acids.

Phosphatidate phosphatase activity was found both in the cytosol and in the microsomal membrane of maturing safflower seeds. The combined and relative activities of these two forms varied with seed maturation. During the period of rapid triacylglycerol accumulation in the cell, most of the phosphatidate phosphatase activity was membrane-bound; at the initial and last stages of seed development when triacylglycerol synthesis was at an insignificant level, the majority of the activity was soluble. The potassium salts of palmitic, stearic and oleic acids, which are the fatty acid products of proplastids, caused the translocation of the cytosolic phosphatidate phosphatase to the microsomal membrane, while laurate and linoleate, which are not products of proplastids, showed no effect. Oleoyl-CoA did not convert the soluble form of the enzyme into the membrane-bound form. The translocation induced by oleate was reversible. The cytosolic phosphatidate phosphatase of safflower seeds was not transferred to the microsomal membranes prepared from soybean, a plant species of Leguminosae, and from rapeseed, a species of Cruciferae, but was transferred to that from sunflower, which belongs to the same family as safflower, Compositae. These observations suggest that in maturing oil seeds the rate of fatty acid synthesis in proplastids may regulate the species-specific translocation of phosphatidate phosphatase between the cytosol and the endoplasmic reticulum membrane where triacylglycerol synthesis occurs and that in turn the translocation of this ambiquitous enzyme could control the rate of triacylglycerol synthesis in the cell.

Biological Transport↗
PubMed1991

Phosphatidate phosphatase from Saccharomyces cerevisiae. Isolation of 45- and 104-kDa forms of the enzyme that are differentially regulated by inositol.

Immunoblot analysis of cell extracts using antibodies specific for the 91-kDa form of membrane-associated phosphatidate phosphatase from Saccharomyces cerevisiae (Lin, Y.-P., and Carman, G.M. (1989) J. Biol. Chem. 264, 8641-8645) revealed the existence of a 45-kDa form of the enzyme. Immunoblot analysis also showed that the 91-kDa form of the enzyme was a proteolytic product of a 104-kDa enzyme. The mitochondrial fraction contained the 45-kDa enzyme, whereas the microsomal fraction contained the 45- and 104-kDa enzymes. In vivo labeling experiments showed that the 104-kDa form of phosphatidate phosphatase was not a precursor of the 45-kDa form of the enzyme. The 45- and 104-kDa forms of phosphatidate phosphatase were purified and characterized. The enzymological properties of both enzymes were similar. However, the phosphatidate phosphatase 45- and 104-kDa proteins differed with respect to their isoelectric points and peptide fragments resulting from V8 proteolysis and cyanogen bromide cleavage. The expression of the phosphatidate phosphatase 45- and 104-kDa enzymes were regulated differentially in cells supplemented with inositol. The addition of inositol to the growth medium resulted in the induction of the phosphatidate phosphatase 45-kDa enzyme. The expression of the 104-kDa enzyme was not affected by inositol. Both forms of phosphatidate phosphatase were induced when cells entered the stationary phase of growth.

Blotting, Western↗
PubMed1990

Kinetic analysis of yeast phosphatidate phosphatase toward Triton X-100/phosphatidate mixed micelles.

A detailed kinetic analysis of purified yeast membrane-associated phosphatidate phosphatase was performed using Triton X-100/phosphatidate mixed micelles. Enzyme activity was dependent on the bulk and surface concentrations of phosphatidate. These results were consistent with the "surface dilution" kinetic scheme (Deems, R. A., Eaton, B. R., and Dennis, E. A. (1975) J. Biol. Chem. 250, 9013-9020) where phosphatidate phosphatase binds to the mixed micelle surface before binding to its substrate and catalysis occurs. Phosphatidate phosphatase was shown to physically associate with Triton X-100 micelles in the absence of phosphatidate, however, the enzyme was more tightly associated with micelles when its substrate was present. The enzyme had 5- to 6-fold greater affinity (reflected in the dissociation constant nKsA/chi) for Triton X-100 micelles containing dioleoyl-phosphatidate and dipalmitoyl-phosphatidate when compared to micelles containing dicaproyl-phosphatidate. The Vmax for dioleoyl-phosphatidate was 3.8-fold higher than the Vmax for dipalmitoyl-phosphatidate, whereas the interfacial Michaelis constant chi KmB for dipalmitoyl-phosphatidate was 3-fold lower than the chi KmB for dioleoyl-phosphatidate. The specificity constants (Vmax/chi KmB) of both substrates were similar which indicated that dioleoyl-phosphatidate and dipalmitoyl-phosphatidate were equally good substrates. Based on catalytic constants (Vmax and chi KmB), dicaproyl-phosphatidate was the best substrate with an 11- and 14-fold greater specificity constant when compared to dioleoyl-phosphatidate and dipalmitoyl-phosphatidate, respectively.

Catalysis↗