Antiviral properties of Ro 31-8959, an inhibitor of human immunodeficiency virus (HIV) proteinase

Ro 31-8959 inhibits the spread of HIV infection and the production of cytopathic effects in cultures of acutely infected cells. IC50 values for these effects are in the range 0.5-6.0 nM and IC90 values are in the range 6.0-30.0 nM. This inhibitor is effective even when added to cultures at a late stage of infection, after syncytia have started to form. Virus antigen, virus particles and virus cytopathic effects can largely be cleared from cultures treated with compound from 3 days until 6 days post infection. In chronically-infected cells, inhibition of virus maturation can be detected after 24 hours' treatment with 10 nM Ro 31-8959. In addition, a significant reduction of the proteolytic processing of p56 to p24 can be demonstrated in these cells with compound at picomolar concentrations. These properties indicate that Ro 31-8959 is highly effective against HIV with the potential to inhibit acute, established acute and chronic infections.

Identification and purification of calcium-independent phospholipase A2 from bovine brain cytosol

Substantial amounts of phospholipase A2 activity were detected in bovine brain cytosol. The major phospholipase A2 activity was present in the precipitate at 40% saturation with solid ammonium sulfate. After the desaltate of the precipitate was loaded onto an Ultrogel AcA 54 gel filtration column, almost all the activity eluted in the void volume when chromatographed without 1 M KCl. However, when buffer with 1 M KCl was used as the eluent, two active peaks were obtained. One peak (peak I) eluted in the void volume, and the other (peak II) eluted with an apparent molecular mass of 39 kDa as compared with standards. The former was active with diacylglycero-3-phosphoethanolamine, whereas the latter was active with both diacylglycero-3-phosphoethanolamine and 1-alk-1'-enyl-2-acylglycero-3-phosphoethanolamine (plasmenylethanolamine). The apparent molecular mass of peak I was estimated to be 110 kDa as compared with standards on an Ultrogel AcA 34 gel filtration column. Both peaks were purified further with a hydrophobic chromatography column (AffiGel 10 coupled with plasmenylethanolamine) and then by high-resolution liquid chromatography on an MA7Q column. The phospholipase A2 obtained from peak II migrated as one main band with a 40-kDa molecular mass and two minor bands with 14- and 25-kDa molecular masses. Phospholipase A2 obtained from peak I eluted as a single peak on high-resolution liquid chromatography but contained two bands with apparent molecular masses of 100 and 110 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of bulimia nervosa: a comparison of interview and self-report questionnaire methods

OBJECTIVE

The main aim of this study was to assess the level of agreement between the Eating Disorders Examination (EDE) and its self-report version (EDE-Q) on key items in a clinic sample of patients with bulimia nervosa. A second objective was to assess the concordance between self-reported and objective body weight in the sample.

METHOD

Sixty females who met DSM-IV criteria for bulimia nervosa (purging type) participated. Fifty-seven of them completed both the EDE and the EDE-Q. Self-reported weight was obtained during a telephone screening interview. Objective weight was subsequently measured at an assessment about a week later.

RESULTS

The EDE generated higher scores than the EDE-Q for the frequency of objective binge and vomiting episodes. The two methods produced equivalent results for subjective binge episodes, laxative and diuretic misuse, and concerns about shape and weight. The self-report method underestimated body weight.

DISCUSSION

These findings suggest that some core features of eating disorders are more accurately assessed using the EDE interview.

Characterization of human chromosomal DNA sequences which replicate autonomously in Saccharomyces cerevisiae

We have characterised two restriction fragments, isolated from a "shotgun" collection of human DNA, which function as autonomously replicating sequences (ARSs) in Saccharomyces cerevisiae. Functional domains of these fragments have been defined by subcloning and exonuclease (BAL 31) deletion analysis. Both fragments contain two spatially distinct domains. One is essential for high frequency transformation and is termed the Replication Sequence (RS) domain, the other, termed the Replication Enhancer (RE) domain, has no inherent replication competence but is essential for ensuring maximum function of the RS domain. The nucleotide sequence of these domains reveals several conserved sequences one of which is strikingly similar to the yeast ARS consensus sequence.

Phosphorylation of purified Novikoff hepatoma topoisomerase I

The purified Novikoff hepatoma nuclear phosphoprotein with a molecular weight of 110 kdalton and pI 8.4, was found to be a type I topoisomerase. When isolated from 32P-labeled Novikoff ascites cells or incubated in vitro with protein kinase, phosphoserine was found to be its major phosphorylated amino acid. The enzymatic activity of topoisomerase I was altered by changes in phosphorylation. Its activity was increased by protein kinase and it was decreased by alkaline phosphatase.

Identification of a ligand binding site in the human neutrophil formyl peptide receptor using a site-specific fluorescent photoaffinity label and mass spectrometry

A novel fluorescent photoaffinity cross-linking probe, formyl-Met-p-benzoyl-L-phenylalanine-Phe-Tyr-Lys-epsilon-N-fluorescei n (fMBpaFYK-fl), was synthesized and used to identify binding site residues in recombinant human phagocyte chemoattractant formyl peptide receptor (FPR). After photoactivation, fluorescein-labeled membranes from Chinese hamster ovary cells were solubilized in octylglucoside and separated by tandem anion exchange and gel filtration chromatography. A single peak of fluorescence was observed in extracts of FPR-expressing cells that was absent in extracts from wild type controls. Photolabeled Chinese hamster ovary membranes were cleaved with CNBr, and the fluorescent fragments were isolated on an antifluorescein immunoaffinity matrix. Matrix-assisted laser desorption ionization mass spectrometry identified a major species with mass = 1754, consistent with the CNBr fragment of fMBpaFYK-fl cross-linked to Val-Arg-Lys-Ala-Hse (an expected CNBr fragment of FPR, residues 83-87). This peptide was further cleaved with trypsin, repurified by antifluorescein immunoaffinity, and subjected to matrix-assisted laser desorption ionization mass spectrometry. A tryptic fragment with mass = 1582 was observed, which is the mass of fMBpaFYK-fl cross-linked to Val-Arg-Lys (FPR residues 83-85), an expected trypsin cleavage product of Val-Arg-Lys-Ala-Hse. Residues 83-85 lie within the putative second transmembrane-spanning region of FPR near the extracellular surface. A 3D model of FPR is presented, which accounts for intramembrane, site-directed mutagenesis results (Miettinen, H. M., Mills, J., Gripentrog, J., Dratz, E. A., Granger, B. L., and Jesaitis, A. J. (1997) J. Immunol. 159, 4045-4054) and the photochemical cross-linking data.

Characterization of the binding site on the formyl peptide receptor using three receptor mutants and analogs of Met-Leu-Phe and Met-Met-Trp-Leu-Leu

The formyl peptide receptor (FPR) is a chemotactic G protein-coupled receptor found on the surface of phagocytes. We have previously shown that the formyl peptide binding site maps to the membrane-spanning region (Miettinen, H. M., Mills, J. S., Gripentrog, J. M., Dratz, E. A., Granger, B. L., and Jesaitis, A. J. (1997) J. Immunol. 159, 4045-4054). Recent reports have indicated that non-formylated peptides, such as MMWLL can also activate this receptor (Chen, J., Bernstein, H. S., Chen, M., Wang, L., Ishi, M., Turck, C. W., and Coughlin, S. R. (1995) J. Biol. Chem. 270, 23398-23401.) Here we show that the selectivity for the binding of different NH(2)-terminal analogs of MMWLL or MLF can be markedly altered by mutating Asp-106 to asparagine or Arg-201 to alanine. Both D106N and R201A produced a similar change in ligand specificity, including an enhanced ability to bind the HIV-1 peptide DP178. In contrast, the mutation R205A exhibited altered specificity at the COOH terminus of fMLF, with R205A binding fMLF-O-butyl > fMLF-O-methyl > fMLF, whereas wt FPR bound fMLF > fMLF-O-methyl approximately fMLF-O-butyl. These data, taken together with our previous finding that the leucine side chain of fMLF is probably bound to FPR near FPR (93)VRK(95) (Mills, J. S., Miettinen, H. M., Barnidge, D., Vlases, M. J., Wimer-Mackin, S., Dratz, E. A., and Jesaitis, A. J. (1998) J. Biol. Chem. 273, 10428-10435.), indicate that the most likely positioning of fMLF in the binding pocket of FPR is approximately parallel to the fifth transmembrane helix with the formamide group of fMLF hydrogen-bonded to both Asp-106 and Arg-201, the leucine side chain pointing toward the second transmembrane region, and the COOH-terminal carboxyl group of fMLF ion-paired with Arg-205.

A secretory protease inhibitor requires androgens for its expression in male sex accessory tissues but is expressed constitutively in pancreas

A full length cDNA clone encoding a mouse prostatic secretory glycoprotein (p12) whose synthesis is dependent upon testicular androgens has been cloned and characterized. The predicted amino acid sequence of p12 shares extensive homology with several members of the Kazal family of secretory protease inhibitors, in particular the pancreatic secretory trypsin inhibitors. In agreement with sequence data, prostatic secretory p12, purified from mouse ventral prostate secretion, exhibits anti-trypsin activity. Steady-state levels of protease inhibitor mRNA in ventral prostate are reduced from approximately 0.06% in normal mice to undetectable after androgen withdrawal but are inducible within 4 h by re-administration of testosterone. Androgen-dependent expression of the secretory protease inhibitor mRNA was also observed in coagulating gland and seminal vesicle. In seminal vesicle, a tissue of different embryonic origin to the prostate, the kinetics of secretory protease inhibitor mRNA loss after castration are not as rapid as in the ventral prostate and coagulating gland. Low-level androgen independent expression was also observed in the pancreas. There appears to be a single gene for this secretory protease inhibitor and yet expression is markedly stimulated by testosterone in the sex accessory tissues and unaffected by this hormone in the pancreas.

Escape mutants of HIV-1 proteinase: enzymic efficiency and susceptibility to inhibition

Genes encoding a number of mutants of HIV-1 proteinase were sub-cloned and expressed in E. coli. The proteinases containing mutations of single residues (e.g., G48V, V82F, I84V and L90M) were purified and their catalytic efficiencies relative to that of wild-type proteinase were examined using a polyprotein (recombinant HIV-1 gag) substrate and several series of synthetic peptides based on the -Hydrophobic * Hydrophobic-, -Aromatic * Pro- and pseudo-symmetrical types of cleavage junction. The L90M proteinase showed only small changes, whereas the activity of the other mutant enzymes was compromised more severely, particularly towards substrates of the -Aromatic * Pro- and pseudo-symmetrical types. The susceptibility of the mutants and the wild-type proteinase to inhibition by eleven different compounds was compared. The L90M proteinase again showed only marginal changes in its susceptibility to all except one of the inhibitors examined. The K(i) values determined for one inhibitor (Ro31-8959) showed that its potency towards the V82F, L90M, I84V and G48V mutant proteinases respectively was 2-, 3-, 17- and 27-fold less than against the wild-type proteinase. Several of the other inhibitors examined form a systematic series with Ro31-8959. The inhibition constants derived with these and a number of other inhibitors, including ABT-538 and L-735,524, are used in conjunction with the data on enzymic efficiency to assess whether each mutation in the proteinase confers an advantage for viral replication in the presence of any given inhibitor.

Cooperativity among calmodulin's drug binding sites

The binding of felodipine, a dihydropyridine Ca2+ antagonist, to calmodulin has been studied by equilibrium dialysis and fluorescence techniques. Analysis using the Hill equation gives a Hill coefficient of 2. A plot of bound [felodipine] vs. free [felodipine]2 gives a Bmax of 1.9 mol/mol and a K0.5 of 22 microM. Two calmodulin antagonists, prenylamine and R24571, which have previously been shown to potentiate the fluorescent enhancement observed when felodipine binds to calmodulin [Johnson, J. D. (1983) Biochem. Biophys. Res. Commun. 112, 787], produce a reduction in Hill coefficient to 0.7 and 1.0, respectively, and account for the observed potentiation of felodipine binding. Titrations of felodipine with calmodulin in the absence and presence of prenylamine and R24571 suggest that these drugs decrease the K0.5 of calmodulin for felodipine by 25-fold. Thus, potentiating drugs (prenylamine and R24571) bind to either of the two felodipine binding sites and, through an allosteric mechanism, result in felodipine binding to the remaining site with greatly enhanced affinity. Two types of potentiating drugs are observed. Prenylamine exhibits a Hill coefficient of 0.8 whereas felodipine, R24571, and diltiazem exhibit Hill coefficients of 2 in their potentiation of felodipine binding. Titrations of felodipine and calmodulin with Ca2+ exhibit cooperativity with a Hill coefficient of 4. Half-maximal binding occurs near pCa 6.0. In the presence of R24571, the calcium dependence of felodipine binding is biphasic, now exhibiting a much higher affinity (pCa 7.6) component. A model is presented to explain the relationship of these various allosterically regulated conformers of calmodulin and their interactions and activation with its target proteins.

Biologically active fluorescent derivatives of spinach calmodulin that report calmodulin target protein binding

Spinach calmodulin (CaM) has been labeled at cysteine-26 with the sulfhydryl-selective probe 2-(4-maleimidoanilino)naphthalene-6-sulfonic acid (MIANS) to produce MIANS-CaM. The interaction of MIANS-CaM with CaM binding proteins was studied by fluorescence enhancement accompanying the protein-protein interactions. MIANS-CaM bound to smooth muscle myosin light-chain kinase with a Kd of 9 nM, causing a 4.6-fold fluorescence enhancement. Caldesmon bound with a Kd of 250 nM, causing a 2-fold fluorescence enhancement. Calcineurin (CaN) bound to MIANS-CaM with a Kd less than 5 nM, causing an 80% increase in fluorescence. On the other hand, binding of the CaM antagonist drugs prenylamine and calmidazolium or the potent peptide antagonist melittin did not alter MIANS fluorescence. MIANS-CaM activated brain cGMP phosphodiesterase and CaN as effectively as unlabeled CaM. Spinach CaM was also labeled with three other sulfhydryl reagents, 6-acryloyl-2-(dimethylamino)naphthalene, (2,5-dimethoxy-4-stilbenyl)maleimide, and rhodamine X maleimide. CaN bound to the highly fluorescent rhodamine X maleimidyl-CaM with a Kd of 1.4 nM, causing a 25% increase in polarization. Both MIANS-CaM and rhodamine X-CaM were used to monitor the Ca2+ dependence of the interaction between CaM and CaN. Half-maximal binding occurred at pCa 6.7-6.8 in the absence of Mg2+, or at pCa 6.3 in the presence of 3 mM Mg2+. In both cases, the dependence of the interaction was cooperative with respect to Ca2+ (Hill coefficients of 1.7-2.0). Use of these fluorescent CaMs should allow accurate monitoring of CaM interactions with its target proteins and perhaps their localization within the cell.

A continuous fluorescence assay for cyclic nucleotide phosphodiesterase hydrolysis of cyclic GMP

The fluorescent 2'-methylanthraniloyl derivative of cyclic GMP undergoes a 45% decrease in fluorescence when it is cleaved by brain phosphodiesterase in the presence of calmodulin. This fluorescence decrease is dependent upon calcium, calmodulin, and phosphodiesterase, and correlates well (r = 0.996) with the disappearance of substrate as monitored by high-performance liquid chromatography. The Kd values determined by this fluorescence method and HPLC suggest that cyclic GMP and its fluorescent derivative exhibit similar kinetic parameters in their hydrolysis.

Androgen regulated expression of a spermine binding protein gene in mouse ventral prostate

A full length cDNA (MP25) encoding the major mouse prostatic secretory glycoprotein (p25), whose expression is androgen dependent, has been cloned and characterised. Steady-state levels of mRNA are decreased approximately 100-fold after 3 days castration but are restored progressively over 4 days with testosterone treatment. The secreted glycoprotein appears to be a spermine binding protein since the nucleotide and predicted amino acid sequence of MP25 shares extensive homology with a spermine binding protein (SBP) found in rat ventral prostate. Genomic clones indicate that there is a single gene for SBP which consists of 4 exons, the first of which is only 11bp in length. The second exon encodes the signal peptide, the third contains a portion of the spermine binding protein unique to the mouse and the largest exon encodes the bulk of the secreted protein.

Protein interactions in the herpes simplex virus type 1 VP16-induced complex: VP16 peptide inhibition and mutational analysis of host cell factor requirements

The herpes simplex virus VP16 protein functions as a potent transcriptional activator and targets DNA sites with the consensus TAATGARAT present in all the viral immediate-early gene promoters. To do so, VP16 directs assembly of a multiprotein complex involving two cellular proteins, host cell factor (HCF) and the Oct-1 DNA-binding transcription factor. To investigate the importance of specific protein-protein interactions to formation of this VP16-induced complex (VIC), we used oligopeptides to prevent VIC assembly. Linear and cyclic peptides corresponding to a region of VP16 previously implicated in complex formation were potent inhibitors of VIC assembly. To further characterize the protein interactions involved, we cloned a human cDNA encoding the minimal VP16 interaction domain of HCF, containing amino acids 1 to 380 [HCF (1-380)]. The REHAYS-based peptides active in preventing VIC assembly were found to specifically block binding of VP16 to HCF (1-380), without affecting VP16-Oct-1 binding. The inhibitory activity of these VP16 peptides was strictly sequence specific for the EHAY residues. Site-directed mutagenesis of the HCF (1-380) domain revealed residues E102 and K105 to be critical determinants in support of VIC formation. Alteration of a single residue in HCF, K105, was shown to virtually abolish complex assembly. Interestingly however, none of the HCF mutants that were impaired in their ability to support complex formation exhibited defects in direct VP16 binding, supporting loss of function at a higher order in complex assembly.

Solubilization, purification and characterization of lysoplasmalogen alkenylhydrolase (lysoplasmalogenase) from rat liver microsomes

Alkenylhydrolase (EC 3.3.2.2; EC 3.3.2.5) has been purified 200-fold to a specific activity of 8.0 mumol/min per mg from rat liver microsomes with 51% of the activity recovered. Purification was accomplished by solubilization of the membrane-associated enzyme with octylglucoside and chromatographic resolution on sequential DEAE cellulose and hydroxylapatite (HPLC) columns in the presence of octylglucoside. The partially purified enzyme, specific for the 2-deacylated plasmalogen, lysoplasmalogen (1-alk-1'-enyl-sn-glycero-3-phosphocholine or -ethanolamine), had no hydrolytic activity with intact plasmalogens or 1-acyl-sn-glycero-3-phosphoethanolamine. Kinetic analyses of enzymic activity demonstrated apparent Km values of 5.5 and 42 microM for 1-alk-1'-enyl-sn-glycero-3-phosphocholine and 1-alk-1'-enyl-sn-glycero-3-phosphoethanolamine, respectively. The Vmax values were 11.7 and 13.6 mumol/min per mg with the choline and ethanolamine substrates, respectively. The optimal pH range was between 6.6 and 7.1 with both substrates; the energy of activation for the purified enzyme was 15,200 cal. The enzyme required no cofactors and was unaffected by low millimolar concentrations of Ca2+, Mg2+, Mn2+ or EDTA. It was inhibited by the sulfhydryl-reacting reagent, p-chloromercuribenzoate. Mono- or diradylglycerophospholipids or sphingomyelin did not affect the enzymic activity at 37 degrees C. Activity of the purified enzyme, destroyed by freezing at -20 degrees C, was preserved if stored at this temperature in the presence of 300-600 microM diradylglycerophosphocholine or 50% glycerol. A continuous spectrophotometric assay, adapted in our laboratory for the assay of liver alkenylhydrolase, facilitated this purification. This is the first reported purification of alkenylhydrolase.

Androgen-regulated expression of secretory protein synthesis in mouse ventral prostate

Two proteins of molecular weights 25 and 12 kDa (p25 and p12 respectively), whose expression is regulated by testosterone, were identified in mouse ventral prostate. An antiserum raised to mouse ventral prostate secretion was used to demonstrate that p25 corresponds to the major secretory glycoprotein in mouse prostatic fluid. This antiserum does not cross-react with the major secretory proteins of the rat ventral prostate. Western blot analysis of mouse ventral prostate proteins using the prostatic secretion antiserum demonstrates that p12 and p25 are detectable at 3 weeks of age, but the maximum level of both proteins is not attained until 5 weeks of age. In addition, synthesis of p25 was also observed in prostate tissue derived from differentiated embryonic urogenital sinus tissue growing as implants under the renal capsule of syngeneic male hosts.

Effect of two novel inhibitors of the human immunodeficiency virus protease on the maturation of the HIV gag and gag-pol polyproteins

The ability of two novel synthetic compounds to inhibit the HIV protease-mediated processing of HIV-1 precursor polyproteins was investigated in an in vitro gag-protease mixed lysate assay system and in an assay using recombinant baculoviruses engineered to express the HIV-1 gag and pol genes in cultured insect cells. With the in vitro mixed lysate assay we have shown that both compounds at 1 microM can completely inhibit the HIV-1 and HIV-2 protease-mediated release of p24 from the HIV-1 gag precursor at pH 5.5 and pH 7.0. In the intracellular baculovirus system these compounds were shown to inhibit the protease-mediated maturation of gag and also the excision of the protease moiety from its precursor.

Intrinsic activity of precursor forms of HIV-1 proteinase

The wild-type -Phe*Pro- bond located at the N-terminus of the mature aspartic proteinase of HIV-1 was replaced by -Ile-Pro- or -Val-Pro-. By this means, processing at this cleavage junction was prevented and so, extended or precursor forms of HIV-proteinase were generated. These constructs were expressed in Escherichia coli, purified therefrom, and their specificity, activity at different pH values and susceptibility to the potent inhibitor, Ro31-8959, was assessed. A hitherto unobserved cleavage junction (at approximately Ala-Phe*Leu-Gln approximately) in the frame-shift region of the gag-pol viral genome was identified and confirmed by demonstrating cleavage of a synthetic peptide corresponding to this region. The implications for viral replication of self-processing at neural pH by proteinase whilst still present (in a precursor form) as a component of the polyprotein are considered; such reactions, however, are still blocked even at pH values as high as 8.0 by Ro31-8959.

In vitro activity of hepatitis B virus polymerase: requirement for distinct metal ions and the viral epsilon stem-loop

Hepadnaviruses have a complex replication cycle which includes reverse transcription of the pregenomic RNA. The initial step in this process in hepatitis B virus (HBV) requires the viral polymerase to engage a highly stable region of secondary structure within the pregenomic RNA termed the epsilon stem-loop. While reverse transcriptases belonging to the retrovirus family use a specific cellular tRNA as primer, HBV polymerase utilizes a tyrosine residue located within its own N terminus. Therefore, the first deoxyribonucleotide is covalently coupled to HBV polymerase prior to extension of the DNA strand by conventional reverse transcription. We have expressed HBV polymerase in a baculovirus and following purification have found it to be active with respect to protein-priming and reverse transcription of copurified RNA. Importantly, we found both of these processes to be critically dependent on the presence of the epsilon stem-loop. The metal ion preferences of HBV polymerase were also investigated for both the protein-priming and reverse transcription activities of this enzyme. Reverse transcription was dependent on magnesium, with an optimal concentration of 5 mM. However, protein-priming was strongly favoured by manganese ions and was optimal at a concentration of 1 mM. Thus, using manganese as sole source of metal ions our activity assay is restricted to the protein-priming event and will allow the search for novel antivirals specifically blocking this unique mechanism.

Phospholipase A2 activities with a plasmalogen substrate in brain and in neural tumor cells: a sensitive and specific assay using pyrenesulfonyl-labeled plasmenylethanolamine

We have developed a new assay method for phospholipase A2 (EC 3.1.1.4.), towards ethanolamine plasmalogen using pyrenesulfonyl-labeled plasmenylethanolamine as the substrate. This procedure is sensitive to about 3 pmol/ml per min and is absolutely specific for plasmalogen. In this method, the product of phospholipase A2, pyrenesulfonyl-labeled lysoplasmalogen, is hydrolyzed to aldehyde and labeled glycerophosphoethanolamine with hydrochloric acid exposure, and after TLC separation, the pyrenesulfonyl-glycerophosphoethanolamine is quantitated spectrofluorometrically. The excitation and emission wave lengths were 340 and 376 nm, respectively. The activity of bovine brain homogenate was 44.1 +/- 6.47 pmol/min per mg protein (n = 3). Among bovine brain subcellular fractions, the distribution and specific activity of the enzymes were highest in cytosol (38.7 +/- 1.58% and 102.6 +/- 16.2 pmol/min per mg protein, n = 3). The activities of neural tumor cells, PC12 pheochromocytoma, Neuro2A and SKNSH neuroblastoma and U1242MG glioblastoma, were 34.4 +/- 6.83 (n = 5), 7.05 +/- 0.97 (n = 4), 5.25 +/- 1.69 (n = 5), and 9.68 +/- 1.35 (n = 4), pmol/min per mg protein (M +/- S.E.M.), respectively.