Phosphorylase kinase, a metal ion-dependent dual specificity kinase

Phosphorylase kinase is shown to be a dual specificity kinase. The specificity of phosphorylation is determined by divalent cation. Mg2+ causes seryl phosphorylation of phosphorylase b, but Mn2+ activates tyrosine phosphorylation of angiotensin II. In contrast to seryl phosphorylation, the tyrosine kinase activity of holoenzyme is not regulated by Ca2+. Preincubation of the holoenzyme with Ca2+, Mg2+ and ATP that causes autophosphorylation activates tyrosine kinase activity. The tyrosyl kinase activity is a property of the gamma subunit. Addition of varying amounts of Mn2+ to a truncated form of the gamma subunit of phosphorylase kinase containing MgATP inhibits serine kinase but activates tyrosine kinase activity. This result along with an oxidative reaction caused by Cu2+ and site-directed mutagenesis of the putative catalytic base inhibiting both serine and tyrosine kinase activity suggest that one active site is involved in both activities. Kinetic studies with Mn2+ and ATP show that Km for nucleotide is not changed with a seryl or tyrosyl substrate. The Vm values are different, and the value for tyrosyl phosphorylation is similar to other tyrosyl kinases. We propose two conformations for the active site; one favors seryl phosphorylation, and the second tyrosyl phosphorylation is caused by the binding of divalent cation at a second metal ion binding site.

Site-directed mutagenesis and deletion of the carboxyl terminus of Escherichia coli ribonucleotide reductase protein R2. Effects on catalytic activity and subunit interaction

Ribonucleotide reductase from Escherichia coli consists of two dissociable, nonidentical homodimeric proteins called R1 and R2. The role of the C-terminal region of R2 in forming the R1R2 active complex has been studied. A heterodimeric R2 form with a full-length polypeptide chain and a truncated one missing the last 30 carboxyl-terminal residues was engineered by site-directed mutagenesis. Kinetic analysis of the binding of this protein to R1, compared with full-length or truncated homodimer, revealed that the C-terminal end of R2 accounts for all of its interactions with R1. The intrinsic dissociation constant of the heterodimeric R2 form, with only one contact to R1, 13 microM, is of the same magnitude as that obtained previously [Climent, I., Sjöberg, B.-M., & Huang, C. Y. (1991) Biochemistry 30, 5164-5171] for synthetic C-terminal peptides, 15-18 microM. We have also mutagenized the only two invariant residues localized at the C-terminal region of R2, glutamic acid-350 and tyrosine-356, to alanine. The binding of these mutant proteins to R1 remains tight, but their catalytic activity is severely affected. While E350A protein exhibits a low (240 times less active than the wild-type) but definitive activity, Y356A is completely inactive. A catalytic rather than structural role for these residues is discussed.

Determination of cinnamic acid and paeoniflorin in traditional Chinese medicinal preparations by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of cinnamic acid in Cinnamomi ramulus and paeoniflorin in Paeoniae radix was established. The samples were separated by a LiChrospher RP-18 column with water-acetonitrile-methanolacetic acid (61:34:5:0.1 or 80:15:5:0.1, v/v) as the mobile phase at a flow-rate of 1.0 ml/min. Cinnamic acid and paeoniflorin were determined by UV detection at 280 and 250 nm, respectively. The method was applied to determine the optimum conditions for the extraction of the traditional Chinese medicinal preparation Huang Chi Chien Chung Tong, which contains Cinnamomi ramulus and Paeoniae radix. The results indicate that the best extraction conditions involved the use of an ultrasonic bath at 60 degrees C for 30 min. In this experiment, butyl paraben and methyl paraben were used as the internal standards for cinnamic acid and paeoniflorin, respectively. A good and reproducible separation of cinnamic acid and paeoniflorin was obtained within 15 min. The method was also applicable to other preparations that contain Cinnamomi ramulus and Paeoniae radix such as Guey Chi Chia Long Ku Muu Li Tong, Kuei Chi Chien Chung Tong and Tang Kuei Chien Chung Tong.

Acetylation phenotype in hypertensive patients

Individual differences in drug-metabolizing capacity may be due to the occurrence of genetic enzyme variants. This study of pharmacogenetics in this paper explores the polymorphic acetylation of hypertensive patients who had taken hydralazine as an antihypertensive drug in the cardiovascular clinic at Chinese Air Force General Hospital. An apparent bimodal distribution of acetylator phenotype was found in 96 subjects (26 slow and 70 fast acetylators) from measuring the percentage of acetylation of sulphamethazine (SMZ) in 6-hr blood, 3-to-6 hr urine samples; and the elimination half-life (t1/2) of SMZ; after administration of SMZ 10 mg/kg. The results might provide a therapeutic index of hydralazine and reduce the probability of drug-induced lupus erythematosus.

Carboxyl-terminal peptides as probes for Escherichia coli ribonucleotide reductase subunit interaction: kinetic analysis of inhibition studies

The active complex of Escherichia coli ribonucleotide reductase comprises two dissociable, nonidentical homodimeric proteins, B1 and B2. When B2 is the varied component, the reductase activity is competitively inhibited by synthetic peptides of varying lengths corresponding to the C-terminus of protein B2. This finding provides the first evidence that the C-terminal peptides and protein B2 share the same binding domain on protein B1. Our data also show that two molecules of peptide can bind to protein B1 with equal affinity. Similar inhibition constants (18 microM) were obtained for peptides containing the C-terminal 20, 30, and 37 residues. When the invariant residue Tyr 356 was omitted, a 2-fold decrease in peptide inhibitory ability was observed. A small peptide, lacking the last 11 residues, had virtually no inhibitory potency. These results, coupled with our previous observations that truncated protein B2, in which one or both polypeptide chains are missing approximately 24 C-terminal residues, had considerably lower or no affinity for B1, suggest that the C-terminal regions are the major determinants in the B1-B2 interaction. In the Appendix, two methods for treatment of kinetic situations pertinent to the ribonucleotide reductase system are presented. One method deals with the determination of kinetic parameters for two components present at comparable levels; the other is concerned with the differentiation of linear and nonlinear competitive inhibition involving the binding of two inhibitor molecules. Both methods should find application to other similar cases.

Mechanisms of the synergistic interactions between organic calcium channel antagonists and various neuromuscular blocking agents

The effects of Mn2+, neomycin and four organic Ca2(+)-channel antagonists (OCA): nicardipine, nifedipine, diltiazem and verapamil on the neuromuscular blocking activities of tubocurarine, succinylcholine (SCh), decamethonium and neomycin were studied in isolated mouse phrenic nerve-diaphragm preparations. The effective concentration of SCh for 50% inhibition (IC50) of single indirect twitch responses were reduced markedly by more than 3-fold when the preparations were pretreated with OCA at 10 microM; the latter alone did not appreciably affect the indirect twitch response or the amplitude of miniature endplate potentials. The neuromuscular blocking effect of decamethonium was also enhanced synergistically by OCA to a similar extent. On the other hand, under the comparable condition. the combined uses of OCA plus tubocurarine or neomycin, neomycin plus tubocurarine or SCh, and Mn2+ plus tubocurarine, SCh or neomycin all resulted in insignificant potentiation. These results suggest that OCA have a specific effect to enhance the agonist effect of depolarizing agents on nicotinic acetylcholine receptors. Nicardipine at 2 microM non-competitively inhibited depolarizations of endplates elicited by SCh and decamethonium and abolished them completely at 10 microM nicardipine. The IC50's in inhibiting endplate potentials and miniature endplate potentials by SCh and decamethonium were also reduced 2 to 3.5-fold by nicardipine. It is inferred that OCA are endowed with a unique capability to allosterically affect the postsynaptic nicotinic acetylcholine receptor, promoting its desensitization liability, hence synergistic interaction with depolarizing agents. Presynaptic effects of OCA are probably not involved.

Cerebrovascular disease in Hong Kong Chinese

Our prospective study of cerebrovascular disease in Hong Kong confirms a previous clinical impression that stroke in the Chinese has a pattern different from that in Caucasians. We studied 540 patients (aged 20-70 years) with stroke. Computed tomography or autopsy was obtained in 86.1% and showed an increase in the proportion with lacunar infarction, striatocapsular infarction, and parenchymal hemorrhage relative to the frequencies in Caucasians. This increase in the incidence of cerebral hemorrhage occurs not only in semicomatose and comatose patients but also in alert patients (16.9%) and those with a lacunar syndrome (12.5%). Our findings suggest that cerebrovascular disease in the Chinese selectively affects small vessels, causing lacunes and hemorrhages. In future community studies on stroke prevalence, researchers should be cautious about interpreting similar prevalence rates as reflecting similar risk factors or pathologies.

Kinetic mechanism of the type II calmodulin-dependent protein kinase: studies of the forward and reverse reactions and observation of apparent rapid-equilibrium ordered binding

The kinetic reaction mechanism of the type II calmodulin-dependent protein kinase was studied by using its constitutively active kinase domain. Lacking regulatory features, the catalytic domain simplified data collection, analysis, and interpretation. To further facilitate this study, a synthetic peptide was used as the kinase substrate. Initial velocity measurements of the forward reaction were consistent with a sequential mechanism. The patterns of product and dead-end inhibition studies best fit an ordered Bi Bi kinetic mechanism with ATP binding first to the enzyme, followed by binding of the peptide substrate. Initial-rate patterns of the reverse reaction of the kinase suggested a rapid-equilibrium mechanism with obligatory ordered binding of ADP prior to the phosphopeptide substrate; however, this apparent rapid-equilibrium ordered mechanism was contrary to the observed inhibition by the phosphopeptide which is not supposed to bind to the kinase in the absence of ADP. Inspection of product inhibition patterns of the phosphopeptide with both ATP and peptide revealed that an ordered Bi Bi mechanism can show initial-rate patterns of a rapid-equilibrium ordered system when a Michaelis constant for phosphopeptide, Kip, is large relative to the concentration of phosphopeptide used. Thus, the results of this study show an ordered Bi Bi mechanism with nucleotide binding first in both directions of the kinase reaction. All the kinetic constants in the forward and reverse directions and the Keq of the kinase reaction are reported herein. To provide theoretical bases and diagnostic aid for mechanisms that can give rise to typical rapid-equilibrium ordered kinetic patterns, a discussion on various sequential cases is presented in the Appendix.

Organic calcium channel antagonists provoke acetylcholine receptor autodesensitization on train stimulation of motor nerve

The effects of nicardipine and other organic Ca2(+)-channel antagonists on the responses induced by indirect train stimulation (3 s, 50-100 Hz) were studied in mouse phrenic nerve diaphragm preparations. Nicardipine at 1-10 microM, which alone did not affect single or tetanic contractions or the amplitude of evoked endplate potentials and spontaneous miniature endplate potentials, caused tetanic contraction to fade completely in the presence of 0.3 microM neostigmine or 50 microM diisopropylfluorophosphate. In combination with these anticholinesterases, nicardipine caused a severe run-down and shortening of endplate potentials in 1-2 s. This effect on endplate potentials was dependent on stimulus frequency and on extracellular Ca2+. The effect was accelerated by intracellular injection of Ca2+, but retarded by injection of EGTA. The amplitudes of miniature endplate potentials and the evoked endplate depolarization were also depressed during repetitive stimulation. On termination of repetitive stimulation, all postsynaptic responses, including evoked endplate potentials, miniature endplate potentials and single twitches, recovered to pre-train level in 3-10 s. These results suggest that the postsynaptic nicotinic receptors had lost the functional activity during repetitive stimulation. The time-courses of the aforementioned changes initiated by repetitive stimulation were similar to the fast phase of desensitization induced by acetylcholine. The irreversible action of alpha-bungarotoxin on acetylcholine receptor was attenuated in the presence of nicardipine and neostigmine if repetitive stimulation was applied. The same effects were observed with other organic Ca2(+)-channel antagonists (diltiazem, verapamil and nifedipine) as well as agonist (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyr idine- 5-carboxylate, BAY K8644), but not with Mn2+, theophylline or caffeine. It is inferred that organic Ca2(+)-channel antagonists interact directly with acetylcholine receptor ion channel, enhance its autodesensitization liability and thus cause extinction of endplate potentials on repetitive stimulation.

Multiple sclerosis amongst Chinese in Hong Kong

A territory-wide investigation of southern Chinese patients with multiple sclerosis (MS) was conducted in Hong Kong. There were 47 patients, 35 of whom were clinically definite (CDMS), 6 laboratory-supported definite (LSDMS) and 6 clinically probable (CPMS). The prevalence rate was 0.88 per 10(5) population, which is of the same order as in other Oriental populations but much lower than in Caucasoid populations. Comparisons with major Oriental and Caucasian series showed essentially the same clinical picture with only minor variations. In one autopsy case, the lesions were found mainly in the optic nerves and spinal cord, with marked softening in addition to the classical demyelination features. In contrast to findings in Caucasians, the detection rate of oligoclonal bands in the cerebrospinal fluid was low (33% in CDMS patients) and there was no association with human leucocyte antigens. The possible implications of these findings on the pathogenesis of MS are discussed.

Nicardipine inhibits axon conduction but causes dual changes of acetylcholine release in the mouse motor nerve

The effects of nicardipine, a dihydropyridine Ca2(+)-channel antagonist, on neuromuscular transmission and impulse-evoked release of acetylcholine were compared with those of nifedipine. In the isolated mouse phrenic nerve diaphragm, nicardipine (50 microM), but not nifedipine (100 microM), induced neuromuscular block, fade of tetanic contraction, and dropout or all-or-none block of end-plate potentials. Nicardipine had no significant effect on the resting membrane potential and the amplitude of miniature end-plate potentials but increased the frequency and caused the appearance of large size miniature potentials. The quantal contents of evoked end-plate potentials were increased. In the presence of tubocurarine, however, nicardipine depressed the amplitude of end-plate potentials. The compound nerve action potential was also decreased. It is concluded that nicardipine blocks neuromuscular transmission by acting on Na+ channels and inhibits axonal conduction. Nicardipine appeared to affect the evoked release of acetylcholine by dual mechanisms, i.e., an enhancement presumably by an agonist action on Ca2+ channels, like Bay K 8644 and nifedipine, and inhibition by an effect on Na+ channels, like verapamil and diltiazem. In contrast with its inactivity on the amplitude of miniature end-plate potentials, depolarization of the end plate in response to succinylcholine was greatly depressed. The contractile response of baby chick biventer cervicis muscle to exogenous acetylcholine was noncompetitively antagonized by nicardipine (10 microM), but was unaffected by nifedipine (30 microM). These results may implicate that nicardipine blocks the postsynaptic acetylcholine receptor channel by enhancing receptor desensitization or by a use-dependent effect.

Type I familial amyloid polyneuropathy in a Chinese family

A Chinese family with at least 3 members having the typical clinical picture of type I familial amyloid polyneuropathy is presented. The pathological features, including the immunohistochemical typing of the amyloid deposits, are described and the literature is briefly reviewed.

Cervical myelopathy due to ossification of the posterior longitudinal ligament. A clinical, radiological and evoked potentials study in six Chinese patients

Six consecutive Chinese patients with cervical myelopathy due to ossification of the posterior longitudinal ligament (OPLL) who presented in a 4 yr period were studied. There were 5 males and 1 female whose mean age at presentation was 67 yrs. The common clinical features were spastic tetraparesis more marked in the lower limbs, spinothalamic and posterior column sensory deficits of varying degree and sphincter disturbance in advanced cases. OPLL was diagnosed on plain radiographs and cord compression ascertained by conventional and computer-assisted myelography. Somatosensory evoked potentials correlated with posterior column signs and appeared to reflect the clinical course following treatment. While the cord pathology in OPLL is similar to that of cervical spondylotic myelopathy (CSM), the pathogenetic mechanism probably differs in one aspect. Compression by OPLL is the determining factor in most cases whereas the combined presence of a congenitally narrow canal and spondylosis is essential for the development of CSM. Other contributory factors include coexisting spondylosis, a congenitally narrow canal, friction between cord and OPLL during neck movement and acute trauma. Cord damage is probably mediated by ischaemia which is due to disturbances of the microcirculation caused by the mechanical factors.

Subcortical arteriosclerotic encephalopathy: a clinical and radionuclide brain scintiscan study

Thirty Chinese patients with clinical and computed tomographic (CT) features of subcortical arteriosclerotic encephalopathy (SAE) were reviewed. It is concluded that the features were sufficiently characteristic for SAE to be considered as a sub-category of cerebrovascular disease and an identifiable cause of dementia in the elderly. Sixteen patients in this series underwent radioisotope brain scintiscan, in which the dynamic radionuclide scintiangiography (RSA) correlated with the clinical course. An increased mean plateau/peak value in the hemispheric curves is seen in the deteriorating patients in contrast to the stable patients.

Beta-thromboglobulin in cerebral infarction

Plasma beta-thromboglobulin (BTG) was significantly elevated in the acute phase of 116 atherosclerotic thrombotic (p less than 0.0001) and 36 cardioembolic (p less than 0.005) infarcts but normal for 96 lacunes compared with controls. This elevation persisted into the 6th week after the acute event. Among atherosclerotic thrombotic infarcts, the acute beta-thromboglobulin level showed a tendency to correlate with infarct size on CT and predicted mortality at 6 weeks. These results suggest that platelet aggregation plays a primary role in the pathogenesis of atherothrombosis.

Cerebral infarct precipitated by praziquantel in neurocysticercosis--a cautionary note

A patient who developed a cerebral infarct during the course of praziquantel therapy for neurocysticercosis is described. Destruction of a large number of cysts by praziquantel followed by a massive inflammatory response was likely to have precipitated the event. Caution on the use of this drug in patients with heavy parasite loads is emphasized.

If a well-stabilized epileptic patient has a subtherapeutic antiepileptic drug level, should the dose be increased? A randomized prospective study

In an attempt to determine whether the dose of an antiepileptic drug should be increased in epileptic patients who were seizure-free and had subtherapeutic serum levels, 79 patients with idiopathic generalized tonic-clonic seizures treated with monotherapy [phenytoin (PHT) or phenobarbital (PB)] and with a subtherapeutic serum level were prospectively studied. Their last seizure was at least 3 months prior to entry, and no patient had any clinical evidence of toxicity. They were randomized to study arm A (keeping the level in the subtherapeutic range) or study arm B (increasing the dose until the level reached and stayed at the therapeutic range). Over a mean follow-up period of 24 months, there was no significant difference between the two study arms in the occurrence of seizures, but arm B patients had an increased incidence of neurotoxic side effects from the dose increment. These results confirm the clinical impression that it is unnecessary to increase the dose of the antiepileptic drug despite a subtherapeutic serum concentration in a relatively well-stabilized patient, thus minimizing the frequency of dose adjustment and the need for expensive therapeutic drug monitoring.

No apparent association between HLA and multiple sclerosis in southern Chinese

HLA-A, -B and -DR antigens have been studied in 34 Chinese patients with multiple sclerosis and 100 normal healthy controls. Unlike patients of other ethnic groups in whom multiple sclerosis is associated with HLA-DR2, there was no obvious association with any HLA antigen in the Chinese patients, although the overall distribution of antigens did not appear typical of the southern Chinese population from which the patients were drawn.

Admission glucose level in relation to mortality and morbidity outcome in 252 stroke patients

In a prospective study to correlate admission glucose level with neurologic outcome in stroke, 252 acute stroke patients without prior disability and admitted within 24 hours of onset of ictus were assessed. The stroke was classified into one of three types--cortical infarct, lacunar infarct, or intracerebral hemorrhage--by clinical, computed tomographic, and necropsy findings. Fifty-one diabetic patients were excluded from the entire cohort to form a nondiabetic category for analysis. We found that admission glucose level showed a significantly higher degree of correlation with mortality and morbidity (measured as arm function, leg function, and activities of daily living) when cortical (n = 118) and lacunar (n = 58) infarcts were pooled compared with when they were assessed separately. For intracerebral hemorrhage (n = 76), admission glucose level correlated with mortality but not morbidity. This trend persisted despite exclusion of diabetic patients. These results are consistent with previous observations of a correlation between a high admission glucose level and the severity of stroke. The importance of segregating cortical from lacunar infarcts, two groups with a different natural history and prognosis, in any future analysis is emphasized.

Dystrophic intracranial calcification: CT evidence of 'cerebral steal' from arteriovenous malformation

Two cases of dystrophic intracranial calcification due to arteriovenous malformations (AVM) are reported. The characteristic distribution is in the watershed areas and away from the AVM. Deposition of calcium on ischaemic brain tissues as a result of 'cerebral steal' by the AVM is the probable pathogenetic mechanism.

Cerebral radionecrosis: is surgery necessary?

Seven patients with cerebral necrosis after radiotherapy for carcinoma of the nasopharynx are presented. The clinical features included seizures and a varying degree of intellectual impairment. In spite of significant mass effect on CT scan, the patients remained alert, ambulatory and independent. We believe that some cases of cerebral necrosis following radiotherapy for extra-cranial neoplasms present in a more benign fashion than has been portrayed in the literature, and in the absence of clinical evidence of raised intracranial pressure, surgical intervention is unnecessary. The importance of careful fractionation of an optimum radiation dose as a preventive measure is emphasised.

Myopathy in acute hypothyroidism

Hypothyroid myopathy has so far been reported in long standing cases of hypothyroidism. We describe two adult patients with myopathy associated with acute transient hypothyroidism. Both presented with severe muscle aches and cramps, stiffness and spasms. Muscle enzymes were markedly elevated and electromyography in one patient showed myopathic features. Histological changes were absent in muscle biopsy, probably because of the short duration of metabolic disturbance. The myopathy subsided promptly when the hypothyroid state was reversed.

Dystrophia myotonica and pregnancy--an instructive case

Two cases of dystrophia myotonica, a mother and her newborn child, are reported. The diagnosis in the mother was only made after seven years and two eventful deliveries. The obstetrical and anaesthetic complications, as well as the neonatal form of dystrophia myotonica, are reviewed.

Cervical spondylotic myelopathy and radiculopathy

A review of the extensive literature on cervical spondylotic myelopathy and radiculopathy shows that the clinical picture and pathology are well defined, and the complex pathogenetic mechanisms are better understood. With recent advances in investigative procedures: computed tomography, magnetic resonance imaging and somatosensory evoked potentials, the diagnosis can be more accurate and the assessment more complete. Careful selection of patients for the appropriate treatment modality (conservative, anterior or posterior surgery) is crucial to the success in management.

When is sensorimotor stroke a lacunar syndrome?

Forty five patients with clear sensorium and no neurological deficits other than unilateral motor and sensory impairment underwent computed tomography (CT). Twenty patients had sensorimotor stroke with impairment of all sensory modalities (type 1). Eight had only impairment of nociceptive sensation (type 2) and 15 had only proprioceptive impairment (type 3). Two patients had sensory impairment in one limb only (type 4). Lacunes were found in patients in the first three groups. However, 80% of those who had hemiparesis and incomplete sensory loss were found to have a lacune or normal CT scan whilst only 33% of those with complete motor or sensory impairment had lacunes. It is proposed that sensorimotor stroke as a lacunar syndrome be best restricted to those with only mild to moderate hemiparesis and sensory impairment in both upper and lower limbs. The degree and extent of sensory and motor involvement may vary, however, possibly dependent on whether the thalamo-geniculate, anterior choroidal or lateral lenticulostriate artery is affected.

Cortical blindness in toxaemia of pregnancy: findings on computed tomography

Two patients with toxaemia of pregnancy presented with cortical blindness. Immediate cranial computed tomography (CT) demonstrated bilateral hypodense areas in the occipital lobes. Both patients underwent Caesarean section for delivery. There was gradual and complete recovery of vision, together with CT documentation of resolution of the cerebral changes, indicative of the reversible nature of the ischaemic lesion.

Claude's syndrome: clinical and computed tomography correlations

A patient with Claude's syndrome (ipsilateral fascicular third nerve palsy with contralateral ataxia) in whom computed tomography demonstrated a discrete infarct in the paramedian rostral mesencephalic tegmentum is reported. The vascular supply of the rostral mesencephalon is discussed.

Prizidilol. Metabolism by cytochrome P-450 and acetyltransferase

The hepatic microsomal cytochrome P-450 enzyme system bound and metabolized the experimental drug prizidilol. Prizidilol bound to two distinct sites on cytochrome P-450. At low concentrations (less than ca 20 microM), prizidilol bound to the substrate binding site of the enzyme and produced a Type I difference spectrum. At higher concentrations (25-190 microM), prizidilol bound to the oxygen binding site of the enzyme and produced a type II difference spectrum. Prizidilol stimulated hepatic microsomal CO-inhibitable NADPH oxidation. Prizidilol metabolism by hepatic microsomes assessed by prizidilol disappearance was inhibited by CO:O2 (80:20; v/v), SKF 525-A and metyrapone. Prizidilol disappearance was monitored using a newly developed TLC assay for prizidilol following derivatization with quinolin-3-al. The apparent binding constants (Ks), maximum extents of binding (delta Amax), Michaelis constants (Km) and maximum velocities (Vmax) for the interaction of prizidilol with hepatic microsomal cytochrome P-450 were assessed in rats pretreated or not with the inducing agents phenobarbital, beta-naphthoflavone and pregnenolone-16 alpha-carbonitrile. For the differently pretreated rats the apparent Ks values for the type I site and the type II site and the apparent Km were ca 3 microM, 150 microM and 2 microM, respectively. Apparent Vmax values varied from 20 to 70 pmol per min per mg microsomal protein. The observed effects of induction on the apparent equilibrium constants and maximum extents of binding and metabolism of prizidilol indicate that the forms of cytochrome P-450 induced by phenobarbital, pregnenolone-16 alpha-carbonitrile or beta-naphthoflavone do not play a major role in the metabolism of prizidilol. Prizidilol was also metabolized by hepatic cytosolic N-acetyltransferase. The apparent Km values for prizidilol and acetyl CoA were 0.8 and 22 microM. Apparent Vmax values were 50 and ca 2 pmol per min per mg protein for partially purified transferase and cytosol, respectively. It is concluded that the rates of oxidation and acetylation of this drug would be expected to be relatively low, being limited by low apparent Vmax values for both oxidation and acetylation.

Herpes zoster and its neurological complications

Ninety-three Chinese patients with cutaneous herpes zoster were seen during a 4-year period. Thoracic zoster occurred most commonly, followed by ophthalmic, cervical and lumbosacral zoster. Neurological complications were present in eleven patients (11.8%), the commonest being Ramsay-Hunt syndrome and segmental limb paresis. The clinical picture, pathogenesis, treatment and outcome of segmental limb paresis, myelitis and delayed contralateral hemiparesis following zoster ophthalmicus are discussed. Nine immunocompromised patients received intravenous adenine arabinoside (vidarabine) or acycloguanosine (acyclovir), and no cutaneous or visceral spread occurred in these patients.

High dose ketoconazole in the treatment of cerebral aspergilloma

A 32-year-old Chinese woman with bilateral occipital aspergilloma was treated successfully with high dose ketoconazole (1200 mg/day) for six months in conjunction with amphotericin B and 5-fluorocytosine. No unacceptable side effects occurred. The use of high dose ketoconazole could be considered in CNS aspergillosis unresponsive to conventional anti-fungal therapy.

Apoplectic intracerebral hemorrhage: an unusual complication of cerebral radiation necrosis

A patient with apoplectic intracerebral hemorrhage from delayed cerebral radionecrosis is reported. The histological changes of abnormal telangiectatic vessels account for the unusual clinical presentation. The pathogenesis and treatment of radionecrosis are discussed, and massive hemorrhage as a complication is emphasized.

Spinal cord compression in multiple myeloma: who gets it?

Of 97 Chinese patients with multiple myeloma seen over a 12-year period, 23.7% were found to have cauda equina or spinal cord compression (SCC). Predictive features for SCC include paraprotein type, hemoglobin level, and the extent of bone lesion at initial hematological diagnosis. A discriminant function derived from this analysis can be used to predict the likelihood of SCC with 79% accuracy. It is postulated that when the cortex is more involved than the medulla in a vertebra, it will predispose to SCC while hemopoiesis is relatively preserved. Our patients presented late with advanced neurological deficit so that treatment was unsatisfactory. It is emphasised that early recognition of back pain and neurological symptoms is essential, as any delay would jeopardize the chance of neurological recovery.

Tuberculous meningitis associated with meningeal tuberculoma

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Cerebral haemorrhage in a urban Chinese population

A prospective study of Chinese patients aged 20-70 years reveals that at least 30.5% of all strokes are due to cerebral haemorrhage. Compared to previous studies in Caucasians, there is both a proportional and absolute increase in cerebral haemorrhage amongst all strokes, alert strokes, or those who presented with just a lacunar syndrome. The cause for this increase is unclear but genetic, dietary, and other environmental factors may be involved.

Reexamination of the activation of yeast proteinase B at pH 5: loss of inhibition effect of proteinase B inhibitors

The activation of yeast proteinase B at pH 5 has been suggested to be due to the degradation of a specific inhibitor for the enzyme, IB, by proteinase A. However, we found that when pepstatin, which completely inhibits proteinase A, was included in the pH 5 activation mixture, the same time-dependent activation of proteinase B was observed. Furthermore, proteinase B preparations that were void of proteinase A activity were still activated by incubation at pH 5. We found that the activation of proteinase B at pH 5 was due primarily to the irreversible loss of inhibitory effect of IB, which can be resolved by isoelectrofocusing into four distinct bands with isoelectric points of 4.6, 6.1, 6.8 and 7.6. These four forms of IB showed varying degrees of stability at pH 5, which may explain some of the differing observations reported in the past.

Interaction between carbamazepine and dextropropoxyphene

Serious side effects may result from the concurrent administration of the usual dosage of carbamazepine and dextropropoxyphene. Three cases are reported and the mechanisms and implications discussed.

Interaction between L-aspartic acid and L-asparaginase from Escherichia coli: binding and inhibition studies

Experiments using equilibrium dialysis and fluorescence quenching provided direct evidence that approximately four moles of L-aspartic acid were bound per mole of tetrameric L-asparaginase from Escherichia coli, with a dissociation constant on the order of 60-160 microM. In addition, a set of weaker binding sites with a dissociation constant in the millimolar range were detected. Kinetic studies also revealed that L-aspartic acid inhibited L-asparaginase competitively, with an inhibition constant of 80 microM at micromolar concentrations of L-asparagine; at millimolar concentrations of the amide, an increase in maximal velocity but a decrease in affinity for L-asparagine were observed. L-Aspartic acid at millimolar levels again displayed competitive inhibition. These and other observations suggest that L-aspartic acid binds not only to the active site but also a second site with lower intrinsic affinity for it. The observed "substrate activation" is most likely attributable to the binding of a second molecule of L-asparagine rather than negative cooperativity among the tight sites of the subunits of this tetrameric enzyme. Further support for L-aspartic acid binding to the active site comes from experiments in which the enzyme, when exposed to various group-specific reagents suffered parallel loss of catalytic activity and in its ability to bind L-aspartic acid. Different commercial preparations of Escherichia coli L-asparaginase were found to contain approximately 2-4 moles of L-aspartic acid; these were incompletely removed by dialysis, but could be removed by transamination or decarboxylation. Efficiency of dialysis increased with increasing pH. Taken together, this set of results is consistent with the existence of a covalent beta-aspartyl enzyme intermediate.

Wilson's disease in a patient presenting with skeletal abnormalities

We present a case with extensive bone and joint involvement in the form of bone fragmentation and osteochondritis dessecans. The case was subsequently documented to be that of Wilson's disease. Biochemical screening was also carried out on the family members and the results of the findings are presented.

Small cerebellar strokes may mimic labyrinthine lesions

Thirty nine cases of cerebellar infarct and haemorrhage were seen over a period of 3 years. Of these, 69% had no impairment of consciousness. Six cases had nystagmus and gait ataxia as their only abnormal signs. Small cerebellar strokes may present with only vertigo, unsteady gait, and unidirectional nystagmus, thus mimicking labyrinthine lesions. Care in managing vertigo attacks in patients with risk factors for cerebrovascular disease appears to be warranted.