pH dependency of the reactions catalyzed by chorismate mutase-prephenate dehydrogenase from Escherichia coli

The variation with pH of the kinetic parameters associated with the mutase and dehydrogenase reactions catalyzed by chorismate mutase-prephenate dehydrogenase has been determined with the aim of elucidating the role that ionizing amino acid residues play in binding and catalysis. The pH dependency of log V for the dehydrogenase reaction shows that the enzyme possesses a single ionizing group with a pK value of 6.5 that must be unprotonated for catalysis. This same group is observed in the V/Kprephenate, as well as in the V/KNAD, profile. The V/Kprephenate profile exhibits a second ionizing residue with a pK value of 8.4 that must be protonated for the binding of prephenate to the enzyme. For the mutase reaction, the V/Kchorismate profile indicates the presence of three ionizing residues at the active site. Two of these residues, with similar pK values of about 7, must be protonated, while the third, with a pK value of 6.3, must be unprotonated. It can be concluded that all three groups are concerned with the binding of chorismate to the enzyme since the maximum velocity of the mutase reaction is essentially independent of pH. This conclusion is confirmed by the finding that the Ki profile for the competitive inhibitor, (3-endo,8-exo)-8-hydroxy-2-oxabicyclo[3.3]non-6-ene-3,5-dicarboxylic acid, shows the same three ionizing groups as observed in the V/Kchorismate profile. By contrast, the Ki profile for carboxyethyldihydrobenzoate shows only one residue, with a pK value of 7.3, that must be protonated for binding of the inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Outcome of psychogenic seizures in children and adolescents compared with adults

We compared outcome of psychogenic seizures documented by video-EEG in 18 nonepileptic children and adolescents (ages 8 to 18; median, 14.5 years old) and 20 adults (ages 25 to 56; median, 34.0 years old). Outcome was significantly better for the younger patients at 1 year, 2 years, and 3 years after diagnosis. At these follow-up times, the percentages of children and adolescents free of psychogenic attacks were 73%, 75%, and 81%; at the same follow-up times, the percentages of adults free of psychogenic attacks were only 25%, 25%, and 40%. Factors leading to better outcome for younger patients may have been different psychological mechanisms at different ages of onset and greater effectiveness with earlier intervention.

Chorismate mutase-prephenate dehydrogenase from Escherichia coli. 2. Evidence for two different active sites

The inhibition of the bifunctional enzyme chorismate mutase-prephenate dehydrogenase by substrate analogues, by the end product, tyrosine, and by the protein modifying agent iodoacetate has been investigated. The purpose of the investigations was to determine if the two reactions catalyzed by the enzyme occur at a single active site or at two separate active sites. Evidence in support of the conclusion that the mutase and dehydrogenase reactions are catalyzed at two similar but distinct active sites comes from the following results: (1) A substrate analogue (endo-oxabicyclic diacid) that inhibits competitively the mutase reaction has no effect on the dehydrogenase reaction. (2) Malonic acid and several of its derivatives act as inhibitory analogues of chorismate in the mutase reaction and of prephenate in the dehydrogenase reaction. However, different dissociation constants for their interaction with the free enzyme are obtained from studies on the mutase and dehydrogenase reactions. (3) The kinetics of the inhibition by tyrosine of the mutase reaction in the presence of NAD differ from those of the dehydrogenase reaction. The results confirm that carboxymethylation with iodoacetate of one cysteine residue per subunit eliminates both mutase and dehydrogenase activities and show that the inactivation of the enzyme activities is due to iodoacetate functioning as an active site directed inhibitor.

Chorismate mutase-prephenate dehydrogenase from Escherichia coli. 1. Kinetic characterization of the dehydrogenase reaction by use of alternative substrates

The bifunctional enzyme involved in tyrosine biosynthesis, chorismate mutase-prephenate dehydrogenase, has been isolated from extracts of a plasmid-containing strain of Escherichia coli K12 and purified to homogeneity by a modified procedure that involves chromatography on both Matrex Blue A and Sepharose-AMP. Detailed studies of the dehydrogenase reaction have been undertaken with analogues of prephenate that act as substrates. The analogues, which included two of the four possible diastereoisomers of 1-carboxy-4-hydroxy-2-cyclohexene-1-propanoate (deoxodihydroprephenate) as well as D- and L-arogenate, were synthesized chemically. As judged by their V/K values, all analogues were poorer substrates than prephenate. The order of their effectiveness as substrates is prephenate greater than one isomer of 1-carboxy-4-hydroxy-2-cyclohexene-1-propanoate greater than L-arogenate greater than other isomer of 1-carboxy-4-hydroxy-2-cyclohexene-1-propanoate greater than D-arogenate. Thus the dehydrogenase activity is dependent on the degree and position of unsaturation in the ring structure of prephenate as well as on the type of substitution on the pyruvyl side chain. With prephenate as a substrate, the reaction is irreversible because it involves oxidative decarboxylation. By contrast, 1-carboxy-4-hydroxy-2-cyclohexene-1-propanoate undergoes only a simple oxidation, and thus, with this substrate, the reaction is reversible. Steady-state velocity data, obtained by varying substrates over a range of higher concentrations, suggest that the dehydrogenase reaction conforms to a rapid equilibrium, random mechanism with 1-carboxy-4-hydroxy-2-cyclohexene-1-propanoate as a substrate in the forward reaction or with the corresponding ketone derivative as a substrate in the reverse direction. The initial velocity patterns obtained by varying prephenate or 1-carboxy-4-hydroxy-2-cyclohexene-1-propanoate over a range of lower concentrations, at different fixed concentrations of NAD, were nonlinear and consistent with a unique model that is described by a velocity equation which is the ratio of quadratic polynomials. An equilibrium constant of 1.4 x 10(-7) M for the reaction in the presence of 1-carboxy-4-hydroxy-2-cyclohexene-1-propanoate indicates that the equilibrium lies very much in favor of ketone production.

Turn It Around: Short-Term Management for Aggression and Anger

1. Although nurses are at considerable risk for assaults, there are few practical and specific guidelines for controlling anger and aggression. 2. A training course was developed to give staff the necessary skills and knowledge to cope with clients who have the potential to become angry and assaultive, or those who have already become violent. 3. Participants in the training course felt more confident in managing potentially violent situations, and they reported relying on methods to de-escalate the situation to halt a sequence that would ultimately lead to violence.

Phorbol ester-induced synaptic facilitation is different than long-term potentiation

The studies described here tested the hypothesis that the changes in synaptic efficacy produced by phorbol esters in hippocampal slices are equivalent to the long-term potentiation (LTP) induced by high-frequency stimulation. In contrast to the extremely stable synaptic potentiation induced by electrical stimulation, the facilitatory effects of phorbol 12,13-diacetate and phorbol 12,13-dibutyrate were transient: washout of the drugs restored normal responses in approximately 1-2 and 2-4 hr for phorbol diacetate and phorbol dibutyrate, respectively. It is noteworthy that the more liposoluble of the phorbol esters required longer washout periods. Robust LTP still occurred in response to high-frequency stimulation after washout of phorbol esters and to a lesser degree during their application. Treatment of slices with H-7, an inhibitor of protein kinase C, did not prevent LTP induction although it significantly affected neuronal excitability and produced effects opposite to those of phorbol esters. Finally, phorbol esters altered responses to repetitive stimulation in a way that could account for the reduced LTP elicited in their presence. These results indicate that the increases in synaptic responses caused by phorbol esters and high-frequency electrical stimulation are quite different and thus do not support the hypothesis that activation of protein kinase C, the presumed target of the phorbol esters, triggers LTP.

Anger control

Anger is a poorly understood but very common emotion. When it is misdirected or uncontrolled it becomes dangerous. An analysis of anger and a treatment paradigm is presented, and we outline a research project in which we are using the approach with a group of mentally handicapped adults.

Speculations on disease states induced by excitatory amino acids

There is much current interest in excitatory amino acids and their receptors because of their postulated involvement in several disorders of the nervous system. They function as neurotransmitters, but can act as neurotoxins in some situations. They have been implicated in the pathogenesis of cerebral hypoxic/ischemic and hypoglycemic damage, in epilepsy, in some degenerative diseases, and in some forms of neurotoxin-induced cerebral dysfunction. These diseases may reflect abnormality in a system which has evolved to provide synaptic plasticity essential for learning and memory. The purpose of this paper is to explore the ramifications of such a hypothesis.

Psychotherapy for bulimia: a controlled study

A psychotherapy study for bulimia is described. The preliminary results of a random allocation control trial comparing cognitive behaviour therapy, behaviour therapy and group psychotherapy with a waiting list control are presented. The results of the first 60 subjects in active treatment are shown. They indicate that all three treatments are effective in dramatically reducing the behavioural symptoms of the bulimia syndrome. There is evidence that cognitive therapy has a greater effect on symptoms of depression and self-esteem. No evidence is yet available on the longterm outcome of the three treatments.

[Effect of growth retardation on the permeability of the blood-brain barrier in the newborn rat exposed to lead]

Postnatal administration of lead to young rats via maternal milk increases the permeability of the blood-brain barrier to trypan blue. However, since this regimen delays postnatal maturation, the question arises whether growth retardation per se could explain the altered permeability to the dye. The present investigation was undertaken to examine this possibility. A first group of newborn rats were fed by dams having free access to normal food; a second group was fed by dams receiving 3% lead as the acetate salt in their food; a third group was fed by dams whose normal diet was restricted to the amount taken daily by dams of the second group. Signs of encephalopathy as shown by urinary incompetence and hind-limb paralysis were observed only in your pups exposed to lead; similarly, only the latter showed increased brain permeability to trypan blue. These results suggest that the altered permeability of the blood-brain barrier in young rats is the direct consequence of lead toxicity and not of growth retardation secondary to a nutritional effect of lead.

Intelligence and inspection time in normal and mentally retarded subjects

The present experiments explore the generality of some recent findings relating IQ to a measure known as Inspection Time (IT)--the exposure duration necessary to judge which of two briefly presented straight lines is the longer. In the first study IT and verbal and performance IQ scores were obtained from a large group of normal six- and seven-year-old children. In contrast to some previous suggestions verbal IQ and full-scale IQ did not correlate significantly with IT, and performance IQ showed only a weak correlation with IT (r = -0.29). In the second experiment IT was found to correlate much more highly with performance IQ in a sample of mentally retarded subjects (r = -0.71). Some possible implications of these results for theories of intelligence and of mental retardation are discussed.

Learning about death: a project report from the Edinburgh University Medical School

A report of a problem-based learning project on the ethics of terminal care, offered as one of the options available to first year MB ChB students in Edinburgh University Medical School. The project formed part of the 'clinical correlation course' in the new curriculum. Six students took part under the supervision of two clinical tutors and a moral philosopher. The course was case-based and practical with students being given the opportunity over a period of eight weeks to meet patients, relatives and hospital staff at a local geriatrics hospital and terminal care home. The main issue studied was the degree of choice available to patients electing to be treated at home, in hospital or in a hospice. Other issues included: pre-death, disposal of the dead, certification of death, communication with relatives and follow-up bereavement services.

Carbenicillin and penicillin G inhibit platelet function in vitro by impairing the interaction of agonists with the platelet surface

Carbenicillin or penicillin G administered in large doses can cause a bleeding diathesis as a result of platelet dysfunction. These antibiotics also inhibit platelet aggregation in vitro, although several-fold larger concentrations of drug are required to demonstrate this effect. We wondered whether these antibiotics might impair platelet function by interfering with the initial step of platelet activation: the binding of agonists to their specific receptors on the platelet surface.Platelet aggregation and [(14)C]serotonin release induced by epinephrine were competitively inhibited by carbenicillin and penicillin G in vitro. At antibiotic concentrations that inhibited platelet function by more than 80%, the affinity of platelet alpha-adrenergic receptors for the alpha-adrenergic antagonist, [(3)H]dihydroergocryptine, and for epinephrine was reduced twofold by carbenicillin and sixfold by penicillin G (P < 0.01). Platelet aggregation and [(14)C]serotonin release stimulated by ADP were also competitively inhibited by these antibiotics. In addition, carbenicillin reduced the incorporation of an ADP affinity label, 5'-p-fluorosulfonylbenzoyl [(3)H]adenosine, into its binding protein in platelet membranes. Moreover, both carbenicillin and penicillin G impaired the interaction of von Willebrand factor with platelets as evidenced by their inhibition of the agglutination of formalin-fixed platelets by ristocetin, snake venom, or bovine factor VIII. These studies demonstrate that carbenicillin and penicillin G inhibit platelet function in vitro by impairing the interaction of several agonists with their specific receptors on the platelet surface membrane. If this were mechanism operative in vivo, it could account for the hemorrhagic as well as the potential antithrombotic effects of these antibiotics.

Carbenicillin and Penicillin G Impair Platelet Function by Inhibiting the Binding of Agonists to the Platelet Surface

Carbenicillin (carb) and penicillin G (pen) inhibit human platelet function in vivo and can cause a bleeding diathesis. Since the mechanism by which these drugs inhibit platelets is unknown, we investigated whether they might interfere with the binding of epinephrine, ADP, or ristocetin (von Willebrand factor) to the platelet surface in vitro. Pen (10 mM) or carb (20 mM) produced a 6-fold decrease in the affinity of receptors on intact platelets for both epinephrine and for the α-adrenergic antagonist, 3U-dihydroer-gocryptine (p < 0.001). Neither antibiotic changed the maximum number of α-adrenergic binding sites per platelet. Pen and carb at these concentrations completely inhibited 14C-serotonin release induced by 1 μM epinephrine and inhibited primary platelet aggregation by 1 μM. Similarly, these antibiotics inhibited aggregation and serotonin release induced by 1 μM ADP and inhibited the covalent binding of an ADP analogue (5'FSO2BZAdo) to its specific binding protein in platelet membranes. Moreover, pen and carb inhibited competitively the agglutination of platelets by ristocetin. Thus, carbenicillin and penicillin G decrease the affinity of a number of distinct platelet receptors for their specific agonists, and this correlates with inhibition of platelet function induced by these agonists. Interaction of these antibiotics with the platelet surface membrane may account for their hemorrhagic as well as their anti-thrombotic activity.