Identification of high levels of type 1 and type 2A protein phosphatases in higher plants.

Extracts of Brassica napus (oilseed rape) seeds contain type 1 and type 2A protein phosphatases whose properties are indistinguishable from the corresponding enzymes in mammalian tissues. The type 1 activity dephosphorylated the beta-subunit of phosphorylase kinase selectively and was inhibited by the same concentrations of okadaic acid [IC50 (concentration causing 50% inhibition) approximately 10 nM], mammalian inhibitor 1 (IC50 = 0.6 nM) and mammalian inhibitor 2 (IC50 = 2.0 nM) as the rabbit muscle type 1 phosphatase. The plant type 2A activity dephosphorylated the alpha-subunit of phosphorylase kinase preferentially, was exquisitely sensitive to okadaic acid (IC50 approximately 0.1 nM), and was unaffected by inhibitors 1 and 2. As in mammalian tissues, a substantial proportion of plant type 1 phosphatase activity (40%) was particulate, whereas plant type 2A phosphatase was cytosolic. The specific activities of the plant type 1 and type 2A phosphatases were as high as in mammalian tissue extracts, but no type 2B or type 2C phosphatase activity was detected. The results demonstrate that the improved procedure for identifying and quantifying protein phosphatases in animal cells is applicable to higher plants, and suggests that okadaic acid may provide a new method for identifying plant enzymes that are regulated by reversible phosphorylation.     

Snake inhibitors of phospholipase A2 enzymes

Phospholipase A₂ (PLA₂) enzymes consist of a large family of proteins which share the same enzymatic function and display considerable sequence homology. These enzymes have been identified and characterised in mammalian tissue and snake venoms. Numerous physiological functions have been attributed to mammalian PLA₂s and they are nontoxic. In comparison, venom PLA₂s are toxic and induce a variety of pharmacological effects that are probably mediated via membrane receptors. Snake PLA₂ inhibitors (PLIα), with a similar structure to the M-type receptor, have been identified as soluble complexes in the serum of viperinae and crotalinae snakes. These inhibitors showed selective binding to crotalid group II PLA₂s and appeared to be restricted to the serum of this snake family. Analysis of PLA₂ binding to recombinant fragments of PLIα indicated that the CRD region was most likely responsible for enzyme inhibition. A second type of inhibitor, PLIβ, has been identified in serum from one viperid snake and consists of a leucine-rich structure. The third type of inhibitor, PLIγ, was found in the serum of five snake families and contains a pattern of cysteine residues that define a three-finger structure. PLIγ inhibitors isolated from the serum of Elapidae, Hydrophidae, Boidae and Colubridae families were able to inhibit a broad range of enzymes including the nontoxic mammalian group IB and IIA PLA₂s, and bee venom group III PLA₂. However, differences in the binding affinities indicated specificity for particular PLA₂s. A different representation has emerged for crotalid and viperid snakes. Their PLIγs did not inhibit bee venom group III, mammalian group IB and IIA enzymes. Furthermore, inhibition data for the γ-type inhibitor from Crotalus durissus terrificus (CICS) showed that this inhibitor was specific for viperid β-neurotoxins and did not inhibit β-neurotoxins from elapids [1]. Further studies are required to determine if this phenomenon is true for all γ-type inhibitors from Crotalidae snakes. The relative distribution of these inhibitors, their specificities and the structural features involved in binding are discussed in this review.     

2,4-Dichlorophenoxyacetic Acid and Related Chlorinated Compounds Inhibit Two Auxin-Regulated Type-III Tobacco Glutathione S-Transferases

Two auxin-inducible glutathione S-transferase (GST, EC 2.5.1.18) isozymes from tobacco (Nicotiana tabacum, White Burley) were partially characterized. GST1-1 and GST2-1 are members of a recently identified new type of plant GST isozymes that we will here refer to as type III. Both enzymes were active, with 1-chloro-2,4-dinitrobenzene as a substrate, when expressed in bacteria as fusion proteins. The apparent Km for 1-chloro-2,4-dinitrobenzene was found to be 0.85 [plus or minus] 0.25 mM for GST1-1 and 0.20 [plus or minus] 0.15 mM for GST2-1. The apparent Km for glutathione was similar for both enzymes, 0.40 [plus or minus] 0.15 mM. The in vitro activity of both enzymes could be inhibited by the synthetic auxin 2,4-dichlorophenoxyacetic acid, with an apparent Ki of 80 [plus or minus] 40 [mu]M for GST1-1 and 200 [plus or minus] 100 [mu]M for GST2-1. The GST1-1 was also inhibited by structurally related substances, such as 2,4-dichlorobenzoic acid, with a roughly similar Ki. The nonchlorinated structures benzoic acid and phenoxyacetic acid did not inhibit. p-Chloroisobutyric acid, or clofibric acid, an auxin-transport inhibitor, was found to be an active inhibitor as well. The strongest inhibitor identified, however, was a phenylacetic acid derivative, ethacrynic acid, which showed an apparent Ki of 5 [plus or minus] 5 [mu]M for both enzymes. This substance is a known inducer as well as a substrate of specific mammalian GSTs. The results presented here indicate that the type III plant GSTs might be involved in the metabolism or transport of chlorinated substances that are structurally related to auxins. The possibility that auxins are endogenous ligands or substrates for GSTs is discussed.     

Domain structure of human 72-kDa gelatinase/type IV collagenase. Characterization of proteolytic activity and identification of the tissue inhibitor of metalloproteinase-2 (TIMP-2) binding regions.

The 72-kDa gelatinase/type IV collagenase, a metalloproteinase thought to play a role in metastasis and in angiogenesis, forms a noncovalent stoichiometric complex with the tissue inhibitor of metalloproteinase-2 (TIMP-2), a potent inhibitor of enzyme activity. To define the regions of the 72-kDa gelatinase responsible for TIMP-2 binding, a series of NH2- and COOH-terminal deletions of the enzyme were constructed using the polymerase chain reaction technique. The full-length and the truncated enzymes were expressed in a recombinant vaccinia virus mammalian cell expression system (Vac/T7). Two truncated enzymes ending at residues 425 (delta 426-631) and 454 (delta 455-631) were purified. Like the full-length recombinant 72-kDa gelatinase, both COOH-terminally truncated enzymes were activated with organomercurial and digested gelatin and native collagen type IV. In contrast to the full-length enzyme, delta 426-631 and delta 455-631 enzymes were less sensitive to TIMP-2 inhibition requiring 10 mol of TIMP-2/mol of enzyme to achieve maximal inhibition of enzymatic activity. The activated but not the latent forms of the delta 426-631 and delta 455-631 proteins formed a complex with TIMP-2 only when excess molar concentrations of inhibitor were used. We also expressed the 205-amino acid COOH-terminal fragment, delta 1-426, and found that it binds TIMP-2. In addition, a truncated version of the 72-kDa gelatinase lacking the NH2-terminal 78 amino acids (delta 1-78) of the proenzyme retained the ability to bind TIMP-2. These studies demonstrate that 72-kDa gelatinases lacking the COOH-terminal domain retain full enzymatic activity but acquire a reduced sensitivity to TIMP-2 inhibition. These data suggest that both the active site and the COOH-terminal tail of the 72-kDa gelatinase independently and cooperatively participate in TIMP-2 binding.     

Inhibition of Retinoic Acid Metabolising Enzymes by 2-(4-aminophenylmethyl)-6-hydroxy-3,4-dihydronaphthalen-1(2H)-one and Related Compounds

In a search for inhibitors of all-trans retinoic acid (RA)-metabolising enzymes as potential agents for the treatment of skin conditions and cancer we have examined 2-(4-aminophenylmethyl)-6-hydroxy-3,4-dihydronaphthalen-1(2H)-one (5). Compound (5) is a moderate inhibitor of RA-metabolising enzymes in mammalian cadaverous tissue microsomes and homogenates as well as RA-induced enzymes in cultured human genital fibroblasts and HaCat cells. Overall (5) was more potent than or equipotent with ketoconazole, a standard inhibitor, in the cadaverous systems but less active towards the RA-induced cell culture systems. Examination of the data suggests that RA-induction generates metabolising enzymes not present in the cadaverous systems, which are more susceptible to inhibition by ketoconazole than (5).     

Inhibition of retinoic acid metabolising enzymes by 2-(4-aminophenylmethyl)-6-hydroxy-3,4-dihydronaphthalen-1(2H)-one and related compounds

In a search for inhibitors of all-trans retinoic acid (RA)-metabolising enzymes as potential agents for the treatment of skin conditions and cancer we have examined 2-(4-aminophenylmethyl)-6-hydroxy-3,4-dihydronaphthalen-1(2H)-one (5). Compound (5) is a moderate inhibitor of RA-metabolising enzymes in mammalian cadaverous tissue microsomes and homogenates as well as RA-induced enzymes in cultured human genital fibroblasts and HaCat cells. Overall (5) was more potent than or equipotent with ketoconazole, a standard inhibitor, in the cadaverous systems but less active towards the RA-induced cell culture systems. Examination of the data suggests that RA-induction generates metabolising enzymes not present in the cadaverous systems, which are more susceptible to inhibition by ketoconazole than (5).     

Engineering the substrate specificity of rhizopuspepsin: the role of Asp 77 of fungal aspartic proteinases in facilitating the cleavage of oligopeptide substrates with lysine in P1.

Rhizopuspepsin and other fungal aspartic proteinases are distinct from the mammalian enzymes in that they are able to cleave substrates with lysine in the P1 position. Sequence and structural comparisons suggest that two aspartic acid residues, Asp 30 and Asp 77 (pig pepsin numbering), may be responsible for generating this unique specificity. Asp 30 and Asp 77 were changed to the corresponding residues in porcine pepsin, Ile 30 and Thr 77, to create single and double mutants. The zymogen forms of the wild-type and mutant enzymes were overexpressed in Escherichia coli as inclusion bodies. Following solubilization, denaturation, refolding, activation, and purification to homogeneity, structural and kinetic comparisons were made. The mutant enzymes exhibited a high degree of structural similarity to the wild-type recombinant protein and a native isozyme. The catalytic activities of the recombinant proteins were analyzed with chromogenic substrates containing lysine in the P1, P2, or P3 positions. Mutation of Asp 77 resulted in a loss of 7 kcal mol-1 of transition-state stabilization energy in the hydrolysis of the substrate containing lysine in P1. An inhibitor containing the positively charged P1-lysine side chain inhibited only the enzymes containing Asp 77. Inhibition of the Asp 77 mutants of rhizopuspepsin and several mammalian enzymes was restored upon acetylation of the lysine side chain. These results suggest that an exploitation of the specific electrostatic interaction of Asp 77 in the active site of fungal enzymes may lead to the design of compounds that preferentially inhibit a variety of related Candida proteinases in immunocompromised patients.     

Allosteric Activation and Contrasting Properties of l-Serine Dehydratase Types 1 and 2

Bacterial l-serine dehydratases differ from mammalian l- and d-serine dehydratases and bacterial d-serine dehydratases by the presence of an iron-sulfur center rather than a pyridoxyl phosphate prosthetic group. They exist in two forms, types 1 and 2, distinguished by their sequence and oligomeric configuration. Both types contain an ASB domain, and the type 1 enzymes also contain an ACT domain in a tandem arrangement with the ASB domain like that in type 1 d-3-phosphoglycerate dehydrogenases (PGDHs). This investigation reveals striking kinetic differences between l-serine dehydratases from Bacillus subtilis (bsLSD, type 1) and Legionella pneumophila (lpLSD, type 2). lpLSD is activated by monovalent cations and inhibited by monovalent anions. bsLSD is strongly activated by cations, particularly potassium, and shows a mixed response to anions. Flouride is a competitive inhibitor for lpLSD but an apparent activator for bsLSD at low concentrations and an inhibitor at high concentrations. The reaction products, pyruvate and ammonia, also act as activators but to different extents for each type. Pyruvate activation is competitive with l-serine, but activation of the enzyme is not compatible with it simply competing for binding at the active site and suggests the presence of a second, allosteric site. Because activation can be eliminated by higher levels of l-serine, it may be that this second site is actually a second serine binding site. This is consistent with type 1 PGDH in which the ASB domain functions as a second site for substrate binding and activation.     

Purification of 2,3-bisphosphoglycerate synthase-phosphatase from pig skeletal muscle

Two enzymes which possess 2,3-bisphosphoglycerate synthase, 2,3-bisphosphoglycerate phosphatase and phosphoglycerate mutase activities have been purified from pig skeletal muscle. One of the enzymes corresponds to type M phosphoglycerate mutase. The other enzyme shows properties similar to those of the 2,3-bisphosphoglycerate synthase-phosphatase present in mammalian erythrocytes. The erythrocyte and the muscle enzyme possess the same molecular (56 000) and subunit (27 000) weights. The synthase, phosphatase and mutase activity ratio is similar in both enzymes, and they are affected by the same inhibitor (glycerate 3-P) and activators (glycolate 2-P, pyrophosphate, sulfite and bisulfite).     

Mammalian lignans and genistein decrease the activities of aromatase and 17beta-hydroxysteroid dehydrogenase in MCF-7 cells

Estrogen plays a major role in breast cancer development and progression. Breast tissue and cell lines contain the necessary enzymes for estrogen synthesis, including aromatase and 17β-hydroxysteroid dehydrogenase (17β-HSD). These enzymes can influence tissue exposure to estrogen and therefore have become targets for breast cancer treatment and prevention. This study determined whether the isoflavone genistein (GEN) and the mammalian lignans enterolactone (EL) and enterodiol (ED) would inhibit the activity of aromatase and 17β-HSD type 1 in MCF-7 cancer cells, thereby decreasing the amount of estradiol (E2) produced and consequently cell proliferation. Results showed that 10 μM EL, ED and GEN significantly decreased the amount of estrone (E1) produced via the aromatase pathway by 37%, 81% and 70%, respectively. Regarding 17β-HSD type 1, 50 μM EL and GEN maximally inhibited E2 production by 84% and 59%, respectively. The reduction in E1 and E2 production by EL and the reduction in E2 production by GEN were significantly related to a reduction in MCF-7 cell proliferation. 4-Hydroxyandrostene-3,17-dione (50 μM) did not inhibit aromatase but inhibited the conversion of E1 to E2 by 78%, suggesting that it is a 17β-HSD type 1 inhibitor. In conclusion, modulation of local E2 synthesis is one potential mechanism through which ED, EL and GEN may protect against breast cancer.     

Inhibition of inorganic pyrophosphatase of animal mitochondria by calcium

Calcium ion is an uncompetitive inhibitor of the inorganic pyrophosphatases of bovine heart and rat liver mitochondria with respect to substrate MgPPi at pH 8.5 and a non-competitive inhibitor of the former enzyme at pH 7.2. The concentration of Ca2+ required to decrease the maximal velocities for both enzymes at pH 8.5, 0.4 mM Mg2+ was about 10 microM. The inhibition results from the binding of two Ca2+ ions to both free enzymes and their complexes with the substrate. The results suggest that Ca2+ regulates pyrophosphatase activity and hence PPi level in mammalian mitochondria.     

Identification of protein phosphatases-1 and 2A and inhibitor-2 in oocytes of the starfish Asterias rubens and Marthasterias glacialis

Protein phosphatases present in the particulate and soluble fractions of oocytes of the starfish Asterias rubens and Marthasterias glacialis have been classified according to the criteria used for these enzymes from mammalian cells. The major protein phosphatase activity in the particulate fraction had very similar properties to protein phosphatase-1 from mammalian tissues, including preferential dephosphorylation of the beta subunit of phosphorylase kinase, sensitivity to inhibitor-1 and inhibitor-2, inhibition of phosphorylase phosphatase activity by protamine and heparin, and retention by heparin-Sepharose. The major protein phosphatase in the soluble fraction had very similar properties to mammalian protein phosphatase-2A, including preferential dephosphorylation of the alpha subunit of phosphorylase kinase, insensitivity to inhibitors-1 and 2, activation by protamine and heparin, and exclusion from heparin-Sepharose. An acid-stable and heat-stable protein was detected in the soluble fraction of starfish oocytes, whose properties were indistinguishable from those of inhibitor-2 from mammalian tissues. It inhibited protein phosphatase-1 specifically, and its apparent molecular mass on SDS polyacrylamide gels was 31 kDa. Furthermore, an inactive hybrid formed between the starfish oocyte inhibitor and the catalytic subunit of mammalian protein phosphatase-1 could be reactivated by preincubation with MgATP and mammalian glycogen synthase kinase-3. The remarkable similarities between starfish oocyte protein phosphatases and their mammalian counterparts are indicative of strict phylogenetic conservation of these enzymes. The results will facilitate further analysis of the role of protein phosphorylation in the control of starfish oocyte maturation by the hormone 1-methyladenine.     

Substrate and inhibitor studies of thermolysin-like neutral metalloendopeptidase from kidney membrane fractions. Comparison with bacterial thermolysin

The inhibitory constants of a series of synthetic N-carboxymethyl peptide inhibitors and the kinetic parameters (Km, kcat, and kcat/Km) of a series of model synthetic substrates were determined for the membrane-bound kidney metalloendopeptidase isolated from rabbit kidney and compared with those of bacterial thermolysin. The two enzymes show striking similarities with respect to structural requirements for substrate binding to the hydrophobic pocket at the S1' subsite of the active site. Both enzymes showed the highest reaction rates with substrates having leucine residues in this position while phenylalanine residues gave the lowest Km. The two enzymes were also inhibited by the same N-carboxymethyl peptide inhibitors. Although the mammalian enzyme was more susceptible to inhibition than its bacterial counterpart, structural variations in the inhibitor molecules affected the inhibitory constants for both enzymes in a similar manner. The two enzymes differed significantly, however, with respect to the effect of structural changes in the P1 and P2' positions of the substrate on the kinetic parameters of the reaction. The mammalian enzyme showed the highest reaction rates and specificity constants with substrates having the sequence -Phe-Gly-Phe- or -Phe-Ala-Phe- in positions P2, P1, and P1', respectively, while the sequence -Ala-Phe-Phe- was the most favored by the bacterial enzyme. The sequence -Gly-Gly-Phe- as found in enkephalins was not favored by either of the enzymes. Of the substrates having an aminobenzoate group in the P2' position, the mammalian enzyme favored those with the carboxyl group in the meta position while the bacterial enzyme favored those with the carboxyl group in the para position.(ABSTRACT TRUNCATED AT 250 WORDS)     

Crystal structure of Trypanosoma cruzi pteridine reductase 2 in complex with a substrate and an inhibitor

Reduced pteridines are required for a number of important cellular functions. Trypanosomatid parasites, unlike their mammalian hosts, are pteridine auxotrophs and salvage the precursor pteridines from the host and reduce them to the respective biologically active tetrahydro forms using parasite-encoded enzymes. These enzymes may offer selective drug targets. In Leishmania, pteridine reductase 1 (PTR1), the primary enzyme for reducing pterins, is also responsible for resistance to antifolate drugs. Typically, PTR1 is more active with fully oxidized biopterin and folate than with their reduced counterparts. We have identified an enzyme, TcPTR2 of Trypanosoma cruzi, which though very similar to PTR1 in its primary sequence, can reduce only dihydrobiopterin and dihydrofolate and not oxidized pteridines. The structures of an inhibitor (methotrexate) and a substrate (dihydrofolate) complex of this enzyme demonstrate that the orientation of the substrate and the inhibitor in the active site of TcPTR2 are different from each other. However, the orientation of each ligand is similar to that of the corresponding ligand in Leishmania major PTR1 complexes.     

Cloning and Characterization of Two Potent Kunitz Type Protease Inhibitors from Echinococcus granulosus

The tapeworm Echinococcus granulosus is responsible for cystic echinococcosis (CE), a cosmopolitan disease which imposes a significant burden on the health and economy of affected communities. Little is known about the molecular mechanisms whereby E. granulosus is able to survive in the hostile mammalian host environment, avoiding attack by host enzymes and evading immune responses, but protease inhibitors released by the parasite are likely implicated. We identified two nucleotide sequences corresponding to secreted single domain Kunitz type protease inhibitors (EgKIs) in the E. granulosus genome, and their cDNAs were cloned, bacterially expressed and purified. EgKI-1 is highly expressed in the oncosphere (egg) stage and is a potent chymotrypsin and neutrophil elastase inhibitor that binds calcium and reduced neutrophil infiltration in a local inflammation model. EgKI-2 is highly expressed in adult worms and is a potent inhibitor of trypsin. As powerful inhibitors of mammalian intestinal proteases, the EgKIs may play a pivotal protective role in preventing proteolytic enzyme attack thereby ensuring survival of E. granulosus within its mammalian hosts. EgKI-1 may also be involved in the oncosphere in host immune evasion by inhibiting neutrophil elastase and cathepsin G once this stage is exposed to the mammalian blood system. In light of their key roles in protecting E. granulosus from host enzymatic attack, the EgKI proteins represent potential intervention targets to control CE. This is important as new public health measures against CE are required, given the inefficiencies of available drugs and the current difficulties in its treatment and control. In addition, being a small sized highly potent serine protease inhibitor, and an inhibitor of neutrophil chemotaxis, EgKI-1 may have clinical potential as a novel anti-inflammatory therapeutic.     

Identification of a novel laser dye substrate of mammalian cytochromes P450: application in rapid kinetic analysis, inhibitor screening, and directed evolution

The author sought to develop a high-throughput activity screening assay to carry out rapid kinetic analysis, inhibitor screening, and directed evolution of cytochrome P450 2C enzymes. Initially, of the 9 fluorescent substrates and 10 P450 2C enzymes tested, several P450 2C enzymes showed > 1 nmol/min/nmol P450 activity in cumene hydroperoxide (CuOOH)-supported reaction with a laser dye, 7-dimethylamino-4-trifluoromethylcoumarin (C152). A high-throughput steady-state kinetic analysis of the human P450 2C8, 2C9, and 2C19 showed 1) k(cat) = 3 to 6 min(-1), 2) K(m, CuOOH) = 100 to 200 microM, and 3) S(50, C152) = 10 to 20 microM in the CuOOH system. In addition, P450 2C9 and 2C19 showed a very high k(ca)t (27 and 38 min(-1), respectively) in the nicotinamide adenine dinucleotide phosphate (NADPH)-supported reaction. Subsequently, when mammalian P450s from the other subfamilies were tested, P450 2B1dH, 2B4dH, 2B5dH, 3A4, and 3A5 exhibited a significant activity in both CuOOH and NADPH systems. Furthermore, a high-throughput activity screening assay using whole-cell suspensions of the human P450 2C8, 2C9, and 2C19 was optimized. Overall, the data suggested that C152 can be used as a model substrate for mammalian P450s in CuOOH-supported reaction to perform rapid kinetic analysis, inhibitor screening, and directed evolution.     

Hydrogen sulfide inhibits high glucose-induced matrix protein synthesis by activating AMP-activated protein kinase in renal epithelial cells

Hydrogen sulfide, a signaling gas, affects several cell functions. We hypothesized that hydrogen sulfide modulates high glucose (30 mm) stimulation of matrix protein synthesis in glomerular epithelial cells. High glucose stimulation of global protein synthesis, cellular hypertrophy, and matrix laminin and type IV collagen content was inhibited by sodium hydrosulfide (NaHS), an H(2)S donor. High glucose activation of mammalian target of rapamycin (mTOR) complex 1 (mTORC1), shown by phosphorylation of p70S6 kinase and 4E-BP1, was inhibited by NaHS. High glucose stimulated mTORC1 to promote key events in the initiation and elongation phases of mRNA translation: binding of eIF4A to eIF4G, reduction in PDCD4 expression and inhibition of its binding to eIF4A, eEF2 kinase phosphorylation, and dephosphorylation of eEF2; these events were inhibited by NaHS. The role of AMP-activated protein kinase (AMPK), an inhibitor of protein synthesis, was examined. NaHS dose-dependently stimulated AMPK phosphorylation and restored AMPK phosphorylation reduced by high glucose. Compound C, an AMPK inhibitor, abolished NaHS modulation of high glucose effect on events in mRNA translation as well as global and matrix protein synthesis. NaHS induction of AMPK phosphorylation was inhibited by siRNA for calmodulin kinase kinase β, but not LKB1, upstream kinases for AMPK; STO-609, a calmodulin kinase kinase β inhibitor, had the same effect. Renal cortical content of cystathionine β-synthase and cystathionine γ-lyase, hydrogen sulfide-generating enzymes, was significantly reduced in mice with type 1 diabetes or type 2 diabetes, coinciding with renal hypertrophy and matrix accumulation. Hydrogen sulfide is a newly identified modulator of protein synthesis in the kidney, and reduction in its generation may contribute to kidney injury in diabetes.     

Interfacial kinetic and binding properties of the complete set of human and mouse groups I,II, V,X, and XII secreted phospholipases A2

Expression of the full set of human and mouse groups I, II, V, X, and XII secreted phospholipases A(2) (sPLA(2)s) in Escherichia coli and insect cells has provided pure recombinant enzymes for detailed comparative interfacial kinetic and binding studies. The set of mammalian sPLA(2)s display dramatically different sensitivity to dithiothreitol. The specific activity for the hydrolysis of vesicles of differing phospholipid composition by these enzymes varies by up to 4 orders of magnitude, and yet all enzymes display similar catalytic site specificity toward phospholipids with different polar head groups. Discrimination between sn-2 polyunsaturated versus saturated fatty acyl chains is <6-fold. These enzymes display apparent dissociation constants for activation by calcium in the 1-225 microm range, depending on the phospholipid substrate. Analysis of the inhibition by a set of 12 active site-directed, competitive inhibitors reveals a large variation in the potency among the mammalian sPLA(2)s, with Me-Indoxam being the most generally potent sPLA(2) inhibitor. A dramatic correlation exists between the ability of the sPLA(2)s to hydrolyze phosphatidylcholine-rich vesicles efficiently in vitro and the ability to release arachidonic acid when added exogenously to mammalian cells; the group V and X sPLA(2)s are uniquely efficient in this regard.     

Sustained phospholipase C stimulation of H9c2 cardiomyoblasts by vasopressin induces an increase in CDP-diacylglycerol synthase 1 (CDS1) through protein kinase C and cFos

Chronic stimulation (24 h) with vasopressin leads to hypertrophy in H9c2 cardiomyoblasts and this is accompanied by continuous activation of phospholipase C. Consequently, vasopressin stimulation leads to a depletion of phosphatidylinositol levels. The substrate for phospholipase C is phosphatidylinositol (4, 5) bisphosphate (PIP₂) and resynthesis of phosphatidylinositol and its subsequent phosphorylation maintains the supply of PIP₂. The resynthesis of PI requires the conversion of phosphatidic acid to CDP-diacylglycerol catalysed by CDP-diacylglycerol synthase (CDS) enzymes. To examine whether the resynthesis of PI is regulated by vasopressin stimulation, we focussed on the CDS enzymes. Three CDS enzymes are present in mammalian cells: CDS1 and CDS2 are integral membrane proteins localised at the endoplasmic reticulum and TAMM41 is a peripheral protein localised in the mitochondria. Vasopressin selectively stimulates an increase CDS1 mRNA that is dependent on protein kinase C, and can be inhibited by the AP-1 inhibitor, T-5224. Vasopressin also stimulates an increase in cFos protein which is inhibited by a protein kinase C inhibitor. We conclude that vasopressin stimulates CDS1 mRNA through phospholipase C, protein kinase C and cFos and provides a potential mechanism for maintenance of phosphatidylinositol levels during long-term phospholipase C signalling.     

Gaucher disease types 1, 2, and 3: differential mutations of the acid beta-glucosidase active site identified with conduritol B epoxide derivatives and sphingosine.

To elucidate the genetic heterogeneity in Gaucher disease, the residual beta-glucosidase in cultured fibroblasts from affected patients with each of the major phenotypes was investigated in vitro and/or in viable cells by inhibitor studies using the covalent catalytic site inhibitors, conduritol B epoxide or its bromo derivative, and the reversible cationic inhibitor, sphingosine. These studies delineated three distinct groups (designated A, B, and C) of residual activities with characteristic responses to these inhibitors. Group A residual enzymes had normal I50 values (i.e., the concentration of inhibitor that results in 50% inhibition) for the inhibitors and normal or nearly normal t1/2 values for conduritol B epoxide. All neuronopathic (types 2 and 3) and most non-Jewish nonneuronopathic (type 1) patients had group A residual activities and, thus, could not be distinguished by these inhibitor studies. Group B residual enzymes had about four- to fivefold increased I50 values for the inhibitors and similarly increased t1/2 values for conduritol B epoxide. All Ashkenazi Jewish type 1 and only two non-Jewish type 1 patients had group B residual activities. The differences in I50 values between groups A and B also were confirmed by determining the uninhibited enzyme activity after culturing the cells in the presence of bromo-conduritol B epoxide. Group C residual activity had intermediate I50 values for the inhibitors and represented a single Afrikaner type 1 patient: this patient was a genetic compound for the group A (type 2) and group B (type 1) mutations. These inhibition studies indicated that: Gaucher disease type 1 is biochemically heterogeneous, neuronopathic and non-Jewish nonneuronopathic phenotypes cannot be reliably distinguished by these inhibitor studies, and the Ashkenazi Jewish form of Gaucher disease type 1 results from a unique mutation in a specific active site domain of acid beta-glucosidase that leads to a defective enzyme with a decreased Vmax.