Purification of adenosine deaminase from chicken-egg yolk by affinity column chromatography

Adenosine deaminase (adenosine aminohydrolase; E.C. 3.5.4.4) has been purified 4686-fold from egg yolk. The procedure developed was used to isolate the enzyme from eight chicken eggs. An easily prepared affinity column employing purine riboside was used as the final step in the purification. The method developed permits the rapid isolation and a high recovery of the protein. The specific activity of the enzyme preparation obtained is 81.4 mU/mg.

Solubilization of A1 adenosine receptor from pig brain: characterization and evidence of the role of the cell membrane on the coexistence of high- and low-affinity states

The present solubilization strategy recognizes the important role of detergent cocktails in the solubilization and subsequent stability of adenosine A1, receptors from pig brain cortical membranes. The 3-[3-(cholamidopropyl)dimethylammonio]-1-propane-sulfonate-digitonin mixture produced the extraction of up to 52% of the receptor with an enrichment of 1.2-fold with respect to crude membranes. The binding activity of the soluble extract was very stable even in the absence of glycerol. In crude membranes the existence of high- and low-affinity states was detected, but in the soluble extract and in the detergent-treated membranes only the high-affinity state was detected. Association-dissociation curves showed that in crude membranes no interconversion between high- and low-affinity sites is produced by the association of the ligand [3H]R-N6-phenylisopropyladenosine. These results suggest that the high- and low-affinity states are different conformations induced by the structure of the membrane. The modulation of the binding activity by (Gpp(NH)p) 5'-guanylylimidodiphosphate and Mg2+ was studied. In crude membranes Gpp(NH)p shifted the high-affinity state to the low-affinity state, whereas the contrary occurred when Mg2+ was used. The effect of both Mg2+ and Gpp(NH)p was also assayed with the soluble extract and with the detergent-treated membranes. In addition to a decrease of the overall binding capacity, Gpp(NH)p promoted a conversion to all low-affinity states in the detergent-treated membranes or to all very-low-affinity sites in the soluble extract. Mg2+ and Gpp(NH)p counteracted their effects in intact membranes, whereas Mg2+ could not reverse the uncoupling effect of Gpp(NH)p with solubilized or detergent-treated membranes. Thus, it is suggested that Mg2+ acts at sites other than guanine-nucleotide-sensitive sites. If high-affinity states correspond to receptor/G protein complexes and low-affinity states correspond to the uncoupled receptor, we should conclude that Mg2+, as well as the loss of membrane integrity, favours the interaction of A1 receptor molecule with G protein.

Expression of multiple alpha 2-adrenergic receptor messenger RNA species in rat tissues

We used a human platelet alpha 2-adrenergic receptor probe to study the tissue distribution and messenger RNA (mRNA) forms of the rat alpha 2-adrenergic receptor. Under stringent conditions of hybridization and washing, we detected an mRNA species of 3.8 kb. The abundance of this form follows the order spleen, kidney, brain stem and cortex, and skeletal muscle and lung and is consistent with the reported abundance and tissue distribution of the alpha 2 receptor activity. A 3.0 kb mRNA form was also detected in cerebral cortex and brain stem and a 4.1 kb mRNA form was observed in kidney under less stringent hybridization conditions. The tissue distribution of the 3.0 kb form is different from that of alpha 1- and beta-adrenergic receptors and the D2 dopaminergic receptor. The mRNA analysis combined with Southern blot analysis of rat and human genomic DNA indicate that: 1) in addition to a 3.8 kb rat alpha 2-adrenergic receptor transcript, there are other mRNA forms in the rat that do not correspond to previously described adrenergic receptor mRNA species and 2) more than one alpha 2-adrenergic receptor gene in the rat is expressed in a tissue-specific manner.

[Isotopic radioangiography in hepatic cirrhosis. Changes induced by somatostatin]

The value of first step isotopic angiography (FSIA) with 99-TC in the study of altered liver kidney and spleen circulation in patients with liver cirrhosis and alcoholic hepatitis is analyzed. This technique is used to evaluate the effect of a 250 mcg IV bolus of somatostatin on the activity/time curve at the three circulatory levels. The ratio of basal hepatic artery/portal flow in cirrhotics was 59 + 11/41 + 11% and 39 + 6/61 + 4 in alcoholic hepatitis, significantly different from normal controls (p less than 0.001). In cirrhotics the degree of alteration in FSIA correlated with the severity of liver disease. Somatostatin significantly improved the ratio of basel hepatic artery/portal flow and diminished the pressure at the root of suprahepatic veins (18.5 +/- - v.s. 16 +/- mmHg, p greater than 0.001). Neither the slopes nor the time of maximum isotopic activity of renal and splenic activity/time curves were modified. We concluded highlighting the clinical value of FSIA as a non invasive test in the study of chronic liver diseases.

Further characterization of adenosine transport in renal brush-border membranes

Adenosine transport has been further characterized in rat renal brush-border membranes (BBM). The uptake shows two components, one sodium-independent and one sodium-dependent. Both components reflect, at least partly, translocation via a carrier mechanism, since the presence of adenosine inside the vesicles stimulates adenosine uptake in the presence as well as in the absence of sodium outside the vesicles. The sodium-dependent component is saturable (Km adenosine = 2.9 microM, Vmax = 142 pmol/min per mg protein) and is abolished at low temperatures. The sodium-independent uptake has apparently two components: one saturable (Km = 4-10 microM, Vmax = 174 pmol/min per mg protein) and one non-saturable (Vmax = 3.4 pmol/min per mg protein, Km greater than 2000 microM). Inosine, guanosine, 2-chloroadenosine and 2'-deoxyadenosine inhibit the sodium-dependent and -independent transport, as shown by trans-stimulation experiments, probably because of translocation via the respective transporter. Uridine and dipyridamole inhibited only the sodium-dependent uptake. Other analogs of adenosine showed no inhibition. The kinetic parameters of the inhibitors of the sodium-dependent component were further investigated. Inosine was the most potent inhibitor with a Ki (1.9 microM) less than the Km of adenosine. This suggests a physiological role for the BBM ecto-adenosine deaminase (enzyme which extracellularly converts adenosine to inosine), balancing the amount of nucleoside taken up as adenosine or inosine by the renal proximal tubule cell.

Adenosine metabolism in kidney slices under normoxic conditions

The effect of adenosine in rat kidney under normoxic conditions has been studied. It is demonstrated that adenosine modulates cell nucleotide levels. HPLC analysis of the purine compounds inside the cell indicates that adenosine improves the ATP/ADP ratio, whereas it diminishes the adenine content. This behaviour is not due to mediation by specific receptors, as agonists at P1 purinoceptors did not have any effect. Further evidence using inosine as well as dipyridamole and deoxycoformycin indicates that all effects are dependent on the previous uptake of adenosine. The origin of free adenine in the kidney has been investigated, and it appears to come from the phosphorolysis of 5'-methylthio-adenosine. This report is the first to describe the activity of methylthioadenosine phosphorylase (E.C. 2.4.2.28) in the kidney. It is concluded that 1) extracellular adenosine improves guinea pig renal function by increasing the ATP level and the ATP/ADP ratio; and 2) there exists a functional pathway in the kidney that produces adenine and AMP coming from methionine and ATP. This latter pathway probably produces spermine and spermidine, which are likely to be important for renal function.

Association of adenosine deaminase with erythrocyte and platelet plasma membrane: an immunological study using light and electron microscopy

Adenosine deaminase has been localized in the plasma membrane of erythrocytes and platelets by means of immunological techniques using light and electron microscopy with cells in suspension. In erythrocytes, adenosine deaminase is associated with the external side of the plasma membrane. In platelets, the enzyme is associated with the external side of the plasma membrane, which is known to extend through the canalicular system of these cells. These results confirm our previous findings, based on biochemical studies, concerning the attachment of the enzyme to cell membranes.

Hormonally inducible phosphorylation of a nuclear pool of ribosomal protein S6

Thyrotropin releasing hormone (TRH) and epidermal growth factor induce the rapid phosphorylation of a basic, chromatin-associated protein present in GH4 rat pituitary cells and also found in primary hepatocyte culture. Cell fraction experiments indicate a nucleolar localization for this basic, chromatin-associated protein. The protein has been purified to homogeneity from rat liver and 23 amino acids of its N-terminal sequence determined. There is complete homology between the sequenced portion of the basic, chromatin-associated protein and the N-terminal sequence of rat ribosomal protein S6. In vivo and in vitro phosphorylation, two-dimensional gel analysis and two-dimensional tryptic phosphopeptide mapping support the identity of the basic, chromatin-associated protein and S6. Our experimental data indicate the existence of a nuclear pool of S6 whose phosphorylation is hormone inducible.

The in vivo survival of human red cells with low oxygen affinity prepared by the osmotic pulse method of inositol hexaphosphate incorporation

The purpose of this study was to determine the posttransfusion survival of low-affinity red cells (RBCs) containing the hemoglobin modifier, inositol hexaphosphate (IHP). An osmotic pulse technique was used to incorporate IHP, a compound that normally does not cross the RBC membrane. Two groups of six volunteers were studied. RBCs were treated under conditions that resulted in a relatively large increase in mean corpuscular volume (delta MCV = 11.8 +/- 4.0, 1 SD) in Group I, but a relatively small increase (delta MCV = 5.5 +/- 1.9) in Group II. The groups had a similar decrease in mean corpuscular hemoglobin (delta MCH = -3.8 +/- 0.9 for Group I and -3.1 +/- 1.1 for Group II). The 24-hour posttransfusion RBC survival, measured with 3 mL of 51Cr-labeled autologous RBCs, correlated with the induced change in oxygen affinity, and larger shifts were associated with poorer survival. An acceptable 75-percent 24-hour posttransfusion survival was achieved for p50 increases up to approximately 15 torr. Cells that survived 24 hours appeared to have a normal lifespan. This study is the first demonstration of adequate survival for human RBCs with a potentially long-lasting decrease in oxygen affinity.

A quantum chemical study of the enzymatic deamination of benzoadenine derivatives. A theoretical model of the interactions occurring between nucleosides and the active site of adenosine deaminase

A theoretical study is presented, where, by using both ab initio and semi-empirical methodologies, the properties of benzoadenine derivatives as substrates of adenosine deaminase are discussed. The results suggest that lin-benzoadenine and lin-benzoadenosine can be recognized with an affinity similar to that of adenosine, but only if they are introduced about 0.12 nm deeper inside the active site of the enzyme than the natural substrate adenosine. This fact implies the existence of non-linear hydrogen bonds inside the active site of adenosine deaminase. Ab initio molecular electrostatic potential values suggest that these hydrogen bonds can exist, and have stability similar to that of linear hydrogen bonds. Finally, the great rate of deamination of lin-benzoadenine, comparable with that of adenosine despite the absence of the ribose, is explained in the context of the hypothesis that the protonation at the N1 atom is the rate-determining step of the whole deamination reaction.

Quantum chemical study of the electronic and conformational characteristics of adenosine and 8-substituted derivatives: functional implications in the mechanism of reaction of adenosine deaminase

A quantum chemical study of 10 substrates of adenosine deaminase is performed. The conformational preference around the glycosidic bond of several 8-substituted derivatives of adenosine is studied using semiempirical modified neglect of diatomic overlap (MNDO) and Austin model 1 (AM1) methods. All the compounds studied show preference for the anti conformation; the syn - anti energetic differences calculated are small and in excellent agreement with experimental data. A relationship between the ab initio molecular electrostatic potential minimum energy of N3 and the syn - anti energetic difference is found. A highly significant relationship is also found between the ab initio net charge over the purine and pyrimidine rings and the logarithm of the maximum rate of deamination (log Vm) of the nucleosides by adenosine deaminase. In contrast, no significant relationship is found between the anti preference of 8-substituted derivatives of adenosine and their log Vm of deamination.

Effects of a vasopressin antagonist with combined antipressor and antiantidiuretic activities in rats with left ventricular dysfunction

These experiments assessed the hemodynamic and aquaretic effects of an arginine vasopressin (AVP) antagonist with dual V1V2-receptor inhibiting properties in rats with congestive heart failure resulting from ischemic cardiomyopathy. The compound d(CH2)5-D-Tyr(Et)VAVP was used in these studies. Rats with limited or extensive myocardial infarcts (i.e., with less than 50% or greater than 66% necrosis of the left ventricular wall, respectively, induced by left coronary ligation) and sham-operated controls received the AVP antagonist (100 micrograms/kg i.v.) 4 weeks later. This agent produced an 18% increase in cardiac output (p less than 0.05) and 13% decrease in systemic vascular resistance in the severely damaged rats, both changes being significantly different from those seen in the normal controls or the rats with limited infarcts. All animals exhibited increases in urinary output of 4-10-fold over baseline. We conclude that the hemodynamic and renal effects of this agent are beneficial in animals with left ventricular dysfunction.

A method for binding parameters estimation of A1 adenosine receptor subtype: a practical approach

Working with pig brain striatum in which A1 and A2 adenosine receptor subtypes coexist, we describe an uncomplicated method for unequivocally obtaining the equilibrium parameters (KD and binding capacity) of A1 receptor without interference from ligand binding to A2 receptor. Also, the equilibrium parameter estimation method we propose avoids the experimental determination of nonspecific binding by the inclusion of the corresponding unknown parameter in the function. This not only saves time but also avoids the use of expensive radioligands in saturation experiments. The method is suitable for any system with two different receptor subtypes for the same physiological ligand, and good estimates of the equilibrium parameters corresponding to the subtype displaying the higher affinity for the ligand can be obtained.

Synthesis and some pharmacologic properties of five novel V1 or V1/V2 antagonists of AVP

Based on [1-(1-mercaptocyclohexaneacetic acid),2-(O-ethyl-D-tyrosine),4-valine]-8-arginine-vasopressin as a model, five new analogues of arginine-vasopressin (AVP) were designed and synthesized. Four of them have in position 1 a large lipophilic substituent, whereas the fifth contains pchloro-D-phenylalanine at position 2. We found that the anti-antidiuretic potency with 1-mercapto-4-methycyclohexaneacetic acid is higher than with 1-mercaptocyclohexaneacetic acid (model peptide) in position 1 and this analogue is among the most potent antagonists of the antidiuretic response to AVP known to date. Upon further increase of the size of substituents, antagonistic potency was significantly decreased or totally eliminated. As for the substitution of p-chloro-D-phenylalanine in position 2, we conclude that this modification leads to substantial decrease of the V2 antagonistic potency.

TEFOOL/2: a program for theoretical drug design on microcomputers

TEFOOL/2, a program written in BASIC, is presented in this paper. The purpose of TEFOOL/2 is to provide people interested in drug design with an easy-to-handle program where some of the most important techniques in QSAR are included. The program permits the selection of the training series, performs regression calculations and searches for optimum substituents. The latter is achieved by using either a Hansch's strategy or geometrical procedures. The program is interactive and can be implemented on an IBM-PC or compatible microcomputer. Although TEFOOL/2 has been developed for its application in drug design studies, its great flexibility makes it suitable for application to any experimental design or optimization process.

[Development of molecular probes for the diagnosis of mycobacteria]

The presence of a repetitive sequence in Mycobacterium bovis DNA was demonstrated. This sequence was also found in M. tuberculosis DNA but was absent in M. kansasii, M. flavescens, M. fortuitum, M. vaccae, M. leprae, M. phlei, M. smegmatis and M. marinum. This repetitive sequence was found to be polymorphic in M. tuberculosis but not in BCG. Dot hybridization analysis suggested that the repetitive sequence could be useful in the identification of pathogenic Mycobacterium in clinical samples.

Bradykinin antagonism and prostaglandins in blood pressure regulation

These experiments were designed to analyze the interaction of a bradykinin antagonist with prostaglandins in blood pressure regulation of normotensive rats. Male Wistar rats, divided into three groups, received a 5-minute intra-arterial infusion of the bradykinin antagonist [( DArgo-Hyp3-Thi5,8-DPhe7]BK-TFA) at 250 micrograms/min. Groups were either intact rats (group I, n = 5), pretreated with indomethacin (group II, n = 10), or pretreated with both indomethacin and prazosin (group III, n = 8). The bradykinin antagonist infusion, which was shown to inhibit exogenous bradykinin by greater than 76% in intact animals, did not alter mean arterial pressure in group I rats despite a twofold increase in norepinephrine and a threefold increase in epinephrine. Group II rats presented a progressive increase in mean arterial pressure during the bradykinin antagonist infusion (14 +/- 3 mm Hg), with no statistically significant change in plasma catecholamines. Group III, with lower baseline mean arterial pressure due to alpha 1-adrenergic blockade, had an increase in mean arterial pressure comparable with group II during bradykinin antagonist infusion (22 +/- 5 mm Hg), confirming that this response was not sympathetically mediated. We conclude that in normotensive rats bradykinin plays a role in blood pressure regulation that is closely linked to that of prostaglandins and that points to a balance between these systems.

Use of implicit methods from general sensitivity theory to develop a systematic approach to metabolic control. I. Unbranched pathways

It is shown that metabolic control theory (MCT), is its present form, is a particular case of general sensitivity theory, which studies the effects of parameter variations on the behavior of dynamic systems. It has been shown that metabolic control theory is obtained from this more general theory for the particular case of steady-state and linear relationships between velocities and enzyme concentrations. In such conditions the relationships between elasticities and flux control coefficients are easily obtained. These relationships are in the form of a matrix product constructed in a priori form. Relationships between combined response coefficients and concentration control coefficients are presented. The use of implicit methodology from general sensitivity theory provides a generalization of MCT, which is applied to unbranched pathways. For this particular case, provided the matrices have been properly constructed, the matrix of global properties (flux and concentration control coefficients) can be obtained by inversion of the matrix of local properties (elasticities). The theorems of MCT (concentration summation, flux summation, flux connectivity, and concentration connectivity) applicable for unbranched pathways are directly obtained by inspection of the matrix product. With these results, the present theoretical basis of MCT is extended with a more structured framework that allows a wider range of application. The results make clearer the relatedness of MCT to the more general approach provided by biochemical systems theory (BST).

Use of implicit methods from general sensitivity theory to develop a systematic approach to metabolic control. II. Complex systems

In the accompanying paper (Cascante et al., this issue) we have used general sensitivity theory to develop a matrix algebra that, in the case of sequential reactions, directly relates global and local properties of a given system. In complex biochemical systems this direct relationship is not possible due to the existence of linear dependencies among fluxes and among metabolite concentrations (conserved aggregate concentrations in BST or moiety-conserved concentrations in MCT). In this paper our matrix algebra is applied to conserved cycles and branched pathways, and it is shown that with minor modifications it again relates global properties to the local properties of the enzymes in the system. In the case of conserved cycles, elasticities become modified due to the existence of linear dependencies among the concentration variables in the cycle. In branched pathways, new matrix elements involving ratios of fluxes appear. With these modifications, one can show that the so-called theorems of metabolic control theory specific to these types of pathways are special cases of more general relationships. Rules for the construction of matrices relating global and local properties are given that apply to an arbitrary system of cycles and branches. The implicit approach developed in these papers, which is a generalization of that used in MCT, allows one to make more direct comparisons with the general explicit approach originally developed in BST.

Heterogeneity of the gradients performed by the freeze-thaw method

Gradients produced by the freeze-thaw method were analyzed at various rates of freezing. The shape of the gradient depended on the rate of freezing. At high rates the pattern did not change but at low rates the steepness of the gradient increased with time. Solutes concentrated at the bottom in a fashion which depended on the density of the solvent and on the rate of freezing. It should also be noted that the gradient was not uniform over the entire surface as the concentration of solute increased near the wall of the test tube.

Theoretical study of the protonation and tautomerization of adenosine, formycin, and their 2-NH2 and 2-F derivatives: functional implications in the mechanism of reaction of adenosine deaminase

A quantum chemical study of adenosine, formycin, and their 2-NH2 and 2-F derivatives is performed. The tautomerism of neutral and protonated species as well as the protonation of adenosine, formycin, and their derivatives are theoretically studied using semiempirical MNDO and AM1, as well as ab initio STO-3G methods. Calculations have been performed on a reduced model, in which the ribose moiety has been substituted by a hydroxy-methyl group. Results indicate that adenosine is mainly protonated at the N1 atom, whereas formycin can be protonated on N1 or N3, depending on the tautomeric form (N8-H or N7-H). The quantum chemical study of the N1-protonated molecules shows that a second protonation of adenosine is mainly on the N3 atom, whereas formycin can be protonated on N8 or N3, depending on the tautomeric form. On the other hand, results indicate that the protonation of formycin and its derivatives at the N1 atom leads to a change in their tautomeric preference from N7-H to N8-H. The importance of both tautomerism and protonation reactions in the mechanism of action of adenosine deaminase is studied by means of a quantitative structure activity relationships strategy. Significant correlations were found between several electronic parameters and the logarithm of the maximum rate of deamination (log Vm) of the studied compounds. For formycin and its derivatives, it was necessary to consider their N8-H tautomeric forms. The electronic parameters giving good correlations were as follows: energy of the minimum of the ab initio molecular electrostatic potential on N1, net charge over purine (pyrazolo-pyrimidine) and pyrimidine rings, and the N1 protonation energy. It must be noted that all these parameters are informative in relation to a proton attack. Adenosine and purine ribosides have been studied largely because of their high biological relevance. They are constituents of nucleic acids, intermediates in secondary metabolism, neuromodulators, and neurohormones. Their analogues have been extensively used because of their wide range of pharmacological effects (1). Formycin A (Fig. 1) is one of the most studied analogues of adenosine. It is a natural product extracted from Nocardia interforma (2) with proven antiviral (3-5), antibiotic (2), immunodepressant (6), antitumor (6), and antimetabolic (5) activities.

Interdependence between cooperativity and control coefficients

Influence of the concentration of internal metabolites on the control coefficient (defined as fractional change in flux per fractional change in enzyme activity) and regulatory properties of a given enzyme have been studied theoretically using a cyclic model of three enzymes. This model is useful to investigate the properties of the flux control coefficient for an enzyme following different rate equations. Enzymes can have high or low values of control coefficient irrespective of the type of kinetic equation, but the results obtained show that the sensitivity of these values to substrate variations is strongly dependent on its rate equation. These results help identify which kinetic equation allows the best control of a given metabolic pathway. These results have been applied to the purine nucleotide cycle. It is demonstrated that the best control of the cycle is reached when the irreversible reaction catalyzed by AMP deaminase follows a rate law that corresponds to a rational function of 2:2 degree with respect to AMP concentration.

Identification and rejection of outliers in enzyme kinetics

A program (AICOUT) for the correct choice of the experimental value and weight for replicate enzyme kinetic determinations is given. It is based on the method of identification of outliers proposed by Kitagawa (Technometrics, 21 (1979) 193-199). The program is written in BASIC and FORTRAN77. The FORTRAN77 version of AICOUT program coupled to a FORTRAN77 version of the non-linear regression program previously published by Canela (Int J Biomed Comput, 15 (1984) 121-130) is given. This joint program leads to an improvement of precision and confidence in the estimated parameters when the suitable strategy is used. This strategy is as follows: (i) the experimental points are selected, (ii) several replicates of each point are performed, (iii) data are analyzed and outliers are rejected, (iv) normal or biweighted regression is carried out.

Determination of the characteristics, properties and homogeneity of rat brain microsomes. Binding of lactate dehydrogenase, malate dehydrogenase and 5' nucleotidase to microsomal membranes

Quantitatively, the amount of microsomes obtained using dimethyl sulfoxide is larger than that obtained from sucrose solutions (Centelles, Franco & Bozal (1986) Biol. Chem. Hoppe Seyler 367, 461-475). In this paper it is demonstrated that from a qualitative point of view they appeared to be indistinguishable with respect to molecular characteristics. Thus, both types of microsomes had the same behaviour in experiments of isopicnic ultracentrifugation with Percoll, isoelectric focusing and gel permeation. In these experiments, the 5'-nucleotidase, lactate dehydrogenase and malate dehydrogenase activities bound to the microsomal fraction were also studied. Lactate and malate dehydrogenase activities were always found in free and membrane-bound form. In contrast, 5'-nucleotidase activity was always encountered bound to microsomal membranes.

Purification and partial characterization of brain adenosine deaminase: inhibition by purine compounds and by drugs

Rat brain adenosine deaminase (E.C. 3.5.4.4.) was purified 667-fold from the supernatant fraction by the following techniques: heat treatment (60 degrees C), fractionation with ammonium sulfate, column chromatography on DEAE-Sepharose, and preparative gel electrophoresis. The purified enzyme was homogeneous by the criterion of polyacrylamide disc gel electrophoresis and isoelectric focusing. Amino acid composition is given. The isoelectric point of the enzyme (5.2) was determined by isoelectric focusing on agarose. The apparent molecular weight was estimated to be 39,000 (Stokes Radius [Rs] = 27.3 A) using a calibrated Sephacryl S-300 column. The study of the influence of the temperature on the initial reaction rates allowed calculation of Ea (8.9 Kcal/mole) and delta H (5.0 Kcal/mole) values. The variation of V and Km with pH suggests the existence of a sulfhydryl group and an imidazole group in the enzyme-substrate complex. The enzyme had a Km (adenosine) of 4.5 X 10(-5) M and was inhibited by inosine, guanosine, adenine, and hypoxanthine but not by other intermediates of purine metabolism. None of the inhibitors were active as substrates. The enzyme was also inhibited by dimethyl sulfoxide and ethanol. Inhibition by ethanol can account partially for the CNS depressant effects of levels 3 and 4 of alcohol intoxication. A number of drugs having therapeutic uses such as sedative, anxiolytic, analgesic, and relaxant are modulators of the enzyme. Among these, lidoflazine, phenylbutazone, and chlordiazepoxide are the most potent as inhibitors (Ki 30, 54, and 83 microM, respectively), whereas medazepam is the most potent as activator (Ka 0.32 mM). Thus, it is concluded that some drugs that inhibit adenosine uptake also modulate adenosine deaminase activity. Besides, since the enzyme is located extracellularly [Franco et al, 1986], these drugs can modulate the physiological effects exerted by extracellular adenosine.

Degradation of adenosine by extracellular adenosine deaminase in the rat duodenum

1. Extracellular degradation of adenosine by adenosine deaminase was studied in the rat duodenum using high performance liquid chromatography (HPLC) and pharmacological techniques. 2. Relaxant responses to adenosine (1-10 microM) were potentiated in a concentration-dependent manner by erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and deoxycoformycin, both of which are inhibitors of adenosine deaminase. 3. Breakdown of adenosine, determined by HPLC, due to incubation with segments of rat duodenum was inhibited by both EHNA and deoxycoformycin. Cytosolic sources of adenosine deaminase were excluded. 4. Relaxant responses to adenosine were also potentiated by the adenosine transport inhibitor dilazep, which did not inhibit adenosine deaminase activity. 5. The extracellular adenosine deaminase activity (4 units/g tissue) was high compared with activity previously determined in other organs.

Subpopulations of T cells in lung biopsies from patients with pigeon breeder's disease

Monoclonal antibodies were used to determine surface phenotypes of T cells in tissue obtained by open lung biopsies from patients with chronic hypersensitivity pneumonitis (pigeon breeder's disease). The results indicate that an increased number of suppressor/cytotoxic cells is present in these patients when compared with the number of helper/inducer cells. These findings, which were present within the interstitium, are consistent with those found in bronchoalveolar lavage of patients with this disease. In addition, in two-thirds of the patients there was a greater total number of helper and suppressor cells than the total count for Pan T cells. A possible interpretation of these findings might be the presence of both markers in the same cell.

A c-erb-A binding site in rat growth hormone gene mediates trans-activation by thyroid hormone

The substance 3,5,3-triiodothyronine (T3) stimulates growth hormone gene transcription in rat pituitary tumour cells. This stimulation is thought to be mediated by the binding of nuclear T3 receptors to regulatory elements 5' to the transcriptional start site. Understanding of the mechanism by which thyroid hormone activates gene transcription has been limited by failure to purify nuclear T3 receptors because of their low abundance, and by the absence of defined T3 receptor-DNA binding sites affecting T3 regulation. Recently, human and avian c-erb-A gene products have been shown to bind thyroid hormone with high affinity and to have a molecular weight and nuclear association characteristic of the thyroid hormone receptor. In the present report, we describe the development of an avidin-biotin complex DNA-binding assay which can detect specific, high-affinity binding of rat pituitary cell T3 receptors to the sequence 5'CAGGGACGTGACCGCA3', located 164 base pairs 5' to the transcriptional start site of the rat growth hormone gene. An oligonucleotide containing this sequence transferred T3 regulation to the herpes simplex virus thymidine kinase promoter in transfected rat pituitary GC2 cells, and specifically bound an in vitro translation product of the human placental c-erb-A gene. The data provide supporting evidence that the human c-erb-A gene product mediates the transcriptional effects of T3 and also that GC2 cell nuclear extracts contain additional factors that modify the binding of pituitary T3 receptors to the rat growth hormone gene T3 response element.

Simulation of the purine nucleotide cycle as an anaplerotic process in skeletal muscle

A computer model of purine nucleotide and citric acid cycles joined through fumarate is given. Steady-state equations corresponding to metabolic enzymes are written based on the information from the literature about their kinetic behavior. Numerical integration of this set of equations is performed and in order to maintain an overall stabilization between the two cycles, enzymatic activities, in the form of V, have been calculated. Sensitivity coefficients for enzymes indicate that the control is exerted, depending upon the intermediate concentrations, and furthermore, it is demonstrated that AMP concentration in muscle should be very low. From stabilization, simulation of exercise conditions has been performed by diminishing [ATP] and increasing accordingly [ADP] and [AMP]. In such conditions the operation of purine nucleotide cycle leads to a considerable increase in the level of citric acid cycle intermediates. Disruption of purine nucleotide cycle by altering some of the three enzymatic steps leads to a lesser increase of these intermediates. The set of results presented seems to confirm the hypothesis that purine nucleotide cycle acts as an anaplerotic process in muscle, as the experimental results of Aragon and Lowenstein (Aragon, J.J., and Lowenstein, J.M. (1980) Eur. J. Biochem. 110, 371-377) suggest.

Distribution of adenosine deaminase in some rat tissues. Inhibition by ethanol and dimethyl sulfoxide

The level of adenosine deaminase in various rat tissues has been tested. The enzyme activity of cytosolic fractions decreased in the following order: lung greater than spleen greater than small intestine greater than stomach greater than kidney greater than heart greater than liver greater than skeletal muscle greater than forebrain greater than cerebellum. The enzyme had identical patterns from tissue to tissue with respect to Km, V, and Ki values for ethanol and for dimethyl sulfoxide, with respect to electrophoretic behaviour and to inhibition by antibodies anti-rat brain adenosine deaminase.

A computer program for enzyme kinetics that combines model discrimination, parameter refinement and sequential experimental design

A method of model discrimination and parameter estimation in enzyme kinetics is proposed. The experimental design and analysis of the model are carried out simultaneously and the stopping rule for experimentation is deduced by the experimenter when the probabilities a posteriori indicate that one model is clearly superior to the rest. A FORTRAN77 program specifically developed for joint designs is given. The method is very powerful, as indicated by its usefulness in the discrimination between models. For example, it has been successfully applied to three cases of enzyme kinetics (a single-substrate Michaelian reaction with product inhibition, a single-substrate complex reaction and a two-substrate reaction). By using this method the most probable model and the estimates of the parameters can be obtained in one experimental session. The FORTRAN77 program is deposited as Supplementary Publication SUP 50134 (19 pages) at the British Library (Lending Division), Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1986) 233, 5.

Discrete cis-active genomic sequences dictate the pituitary cell type-specific expression of rat prolactin and growth hormone genes

The anterior pituitary gland, which is derived from a common primordium originating in Rathke's pouch, contains phenotypically distinct cell types, each of which express discrete trophic hormones: adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), prolactin, growth hormone, and follicle stimulating hormone (FSH)/luteinizing hormone (LH). The structurally related prolactin and growth hormone genes, which are evolutionarily derived from a single primordial gene, are expressed in discrete cell types--lactotrophs and somatotrophs, respectively--with their expression virtually limited to the pituitary gland. The pituitary hormones exhibit a temporal pattern of developmental expression with rat growth hormone and prolactin characteristically being the last hormones expressed. The reported co-expression of these two structurally related neuroendocrine genes within single cells prior to the appearance of mature lactotrophs, in a subpopulation of mature anterior pituitary cells, and in many pituitary adenomas raises the possibility that the prolactin and growth hormone genes are developmentally controlled by a common factor(s). We now report the identification and characterization of nucleotide sequences in the 5'-flanking regions of the rat prolactin and growth hormone genes, respectively, which act in a position- and orientation-independent fashion to transfer cell-specific expression to heterologous genes. At least one putative trans-acting factor required for the growth hormone genomic sequence to exert its effects is apparently different from those modulating the corresponding enhancer element(s) of the prolactin gene because a pituitary 'lactotroph' cell line producing prolactin but not growth hormone selectively fails to express fusion genes containing the growth hormone enhancer sequence.

Kinetics of the 5'-nucleotidase and the adenosine deaminase in subcellular fractions of rat brain

Suspensions of rat brain microsomes, synaptosomes, and synaptic vesicles were able to convert adenosine to inosine by means of adenosine deaminase. Isosbestic points of this transformation, at 222, 250 and 281 nm, remained unchanged with time-course. This fact suggests that adenosine deaminase (ADA, E.C. 3.5.4.4) is located on the surface of the vesicles whereas purine nucleoside phosphorylase (PNP, E.C. 2.1.2.4) is located inside the vesicles. Kinetic parameters of the particulate 5'-nucleotidase (5'N, E.C. 3.1.3.5) and adenosine deaminase were analogous to those of the cytosolic enzymes. These results suggest that soluble and particulate enzymes represent different pools of the same molecular species.

An improved method for the preparation of rat brain microsomes

The rat brains homogenized with different media (sucrose, ethylene glycol, dimethyl sulfoxide and urea) yielded different amounts of microsomal fractions. The dielectric constant, density and viscosity of the homogenization media did not correlate with the amount of microsomes separated by differential centrifugation. The homogenization media containing dimethyl sulfoxide were the most efficient for the isolation of rat brain microsomes. The increase in the yield was up to 4-fold when 50% (v/v) dimethyl sulfoxide was employed. Microsomes isolated in this manner were analogous to those obtained from isotonic sucrose solution, as was demonstrated by their chemical and enzymatic (5'-nucleotidase, adenosine deaminase, guanine deaminase, purine-nucleoside phosphorylase, lactate, malate and glutamate dehydrogenases, amine oxidase fumarate hydratase, acid and alkaline phosphatase, acetylcholinesterase, NADPH-cytochrome c reductase, catalase and thiamine-diphosphatase) characterization.

Enzymes of the purine metabolism in rat brain microsomes

Rat brain microsomes, when they are suspended in moderate ionic strength medium, released enzyme activities of lactate dehydrogenase (LDH, E.C.1.1.1.27), malate dehydrogenase (MDH, E.C.1.1.1.37), adenosine deaminase (ADA, E.C.3.5.4.4), guanine deaminase (GAH, E.C.3.5.4.3), and purine nucleoside phosphorylase (PNP, E.C.2.1.2.4). The activities released decreased when the saline concentration of the medium was increased and the opposite occurred when 50 mM, pH 7.4 sodium phosphate medium was used. Rat brain microsomes that had been extracted previously by moderate ionic strength solutions still had activities of all the enzymes tested, and released these activities upon sonication or deoxycholate (DOC) treatment. The proportion of the activity released was similar for all the enzymes. DOC treatment released higher enzymic activities and a smaller amount of protein than sonication did. The proportion of activities released was similar to that found in the 105,000 g supernatant. The suspension of microsomes still retained activities of the above-mentioned enzymes after consecutive extractions with increasing concentrations of detergent solutions (DOC and Triton X-100). The amount of enzymic activities released from the microsomes by sonication or DOC treatment did not depend on the protein composition of the homogenization medium. Thus, on increasing the enzyme concentration in the homogenization medium, the activities released did not increase in parallel. The set of results obtained showed that the microsomal fraction is as useful as the cytosolic one for studying purine catabolism in rat brain. Furthermore, the conditions in which purine enzymes are attached to the microsomal fraction are probably closer to "in vivo" conditions than those in which these enzymes are found in the soluble fraction.

Heterogeneous localization of some purine enzymes in subcellular fractions of rat brain and cerebellum

The activity of guanine deaminase (GAH, E.C.3.5.4.3) was lower in rat cerebellum soluble and microsomal fractions than in rat brain subfractions. Adenosine deaminase (ADA, E.C.3.5.4.4) activity was released in higher proportion than guanine deaminase, purine nucleoside phosphorylase (PNP, E.C.2.1.2.4), 5'-nucleotidase (5'N, E.C.3.1.3.5), and lactate (LDH, E.C. 1.1.1.27) and malate (MDH, E.C. 1.1.1.37) dehydrogenase in press-juices of rat brain. Furthermore, nerve ending-derived fractions (synaptosomes and synaptic vesicles) showed an enrichment of adenosine deaminase and also of 5'-nucleotidase. The action of deoxycholate over the subfractions did not increase the activity of either enzyme. The contrary occurred with the remaining enzymes studied. Thus, it is possible that one set of enzymes are located on the surface of the particulate vesicles, whereas another set are located inside these vesicles, suggesting a compartmentation of purine catabolic enzymes in different areas of the central nervous system.

Enzyme kinetic studies from progress curves

A method is described for fitting the velocities obtained from progress curves to a steady-state rate equation. It is based on the method of Markus & Plesser [(1981) in Kinetic Data Analysis: Design and Analysis of Enzyme and Kinetic Data (Edrenyi, ed.), pp. 317-339, Plenum Press, New York]. The obstacle of needing good initial estimates of kinetic parameters is removed by using the parameters provided graphically by a minor modification of the method of Yun & Suelter [(1977) Biochim, Biophys. Acta 480, 1-13]. This progress-curved-based method allows the same discrimination among rival models as do the initial-velocity-based methods, with a great saving of experimental time. The BASIC and FORTRAN 77 programs are deposited as Supplementary Publication SUP 50132 (17 pages) at the British Library (Lending Division), Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1986) 233, 5-6.