Reversible phosphorylation as a controlling factor for sustaining calcium oscillations in HeLa cells: Involvement of calmodulin-dependent kinase II and a calyculin A-inhibitable phosphatase

The role of reversible phosphorylation in histamine-induced Ca2+ oscillations in HeLa cells has been investigated by using various activators and inhibitors of protein kinases and phosphatases. Electroporation was employed to introduce impermeable materials into single cells, which proved to be a useful and convenient tool. Of the kinases examined, cAMP-dependent kinase, protein kinase C, and calmodulin-dependent kinase II (CaMK II), only CaMK II was essential. When added during oscillations, both W-7, a calmodulin antagonist, and KN-62, a specific CaMK II inhibitor, caused one large Ca2+ spike before halting the process. Introduction of the Ca2+/calmodulin-independent catalytic domain of CaMK II into the cells forestalled their response to histamine. These results show that intracellular Ca2+ cannot oscillate when CaMK II is locked in either the inactive or the stimulated state. External Ca2+ electroporated into cells preloaded with the catalytic domains was quickly removed (but not when the cells were pretreated with the endoplasmic reticulum Ca(2+)-ATPase inhibitor, tapsigargin), indicating that the ATP-driven Ca2+ pump was somehow activated by CaMK II. Protein phosphatase inhibitors calyculin A and okadaic acid abolished ongoing oscillations and, when added at low concentrations, prolonged the interspike interval. Immunoprecipitation experiments with 32P(i)-labeled cells provided the first evidence that inositol 1,4,5-trisphosphate receptor (IP3R) was phosphorylated by CaMK II in vivo. The extent of phosphorylation was increased in the presence of histamine, significantly enhanced by calyculin A, and greatly reduced by W-7. Our observations are consistent with the concept that repetitive phosphorylation-dephosphorylation cycles regulating IP3R and Ca2+ pumps are a controlling factor for sustained Ca2+ oscillations in HeLa, and possibly other, cells.

Dependence of Mos-induced Cdc2 activation on MAP kinase function in a cell-free system

The progression of G2-arrested Xenopus laevis oocytes into meiotic M-phase is accompanied by the nearly simultaneous activation of p42 MAP kinase and Cdc2/cyclin B. This timing raises the possibility that the activation of one kinase might depend upon the other. Here we have examined whether Cdc2 activation requires p42 MAP kinase function. We have reconstituted Mos-induced Cdc2 activation in cell-free Xenopus oocyte extracts, and have found that Mos-induced Cdc2 activation requires active p42 MAP kinase, is inhibited by a MAP kinase phosphatase and is independent of protein synthesis. These findings indicate that p42 MAP kinase is an essential component of the M phase trigger in this system.

A general method for the spatially defined immobilization of biomolecules on glass surfaces using "caged" biotin

A method has been developed to spatially define the immobilization of proteins on surfaces using the classic avidin-biotin link, for which a wide variety of biochemical reagents are commercially available. A derivative of biotin bearing a photoremovable nitrobenzyl group (MeNPOC-biotin) has been prepared in a form suitable for simple linkage to biomolecules and surfaces. It has been used to functionalize bovine serum albumin (BSA) to form MeNPOC-biotin-BSA, which can then be coated onto glass. On photolithographic patterning of the surface, biotins are freed in the irradiated areas, permitting avidin to be localized at the irradiated sites. Subsequent addition of a biotinylated molecule permits its site-specific localization. Patterning of a biotinylated antibody and dye-labeled avidins or streptavidin using this reagent has been demonstrated by fluorescence microscopy.

Systemic amyloidosis with initial polyneuropathy

We report a case of systemic amyloidosis with the initial sign of polyneuropathy. The patient eventually developed heart failure, macroglossia, and ecchymoses 6 years later. Biopsies from the sural nerve and normal-looking skin both proved the existence of amyloid.

A Mg(2+)-dependent, Ca(2+)-inhibitable serine/threonine protein phosphatase from bovine brain

The Mg(2+)-dependent serine/threonine protein phosphatases, also known as type 2C phosphatases (PP2C), belong to a gene family distinct from the other serine/threonine phosphatases and tyrosine phosphatases. Here we report the purification to apparent homogeneity of a novel Mg(2+)-dependent, Ca(2+)-inhibitable serine/threonine protein phosphatase from bovine brain. It is a type 2C enzyme in view of its Mg2+ requirement, resistance to okadaic acid and calyculin A, inability to use phosphorylase alpha as substrate, and a segment of amino acid sequence typical of all PP2C type phosphatases known to date. However, it differs from the other PP2C enzymes, particularly the mammalian PP2C alpha and -beta isoforms, in that its molecular weight, 76,000, is considerably larger and that it is inhibited by Ca2+, NaF, and polycations, but not by orthovanadate. The Ca2+ inhibition may not be related to its cellular regulation because of Ki values in the 20-90 microM range, but this property permits distinction of this enzyme from the other phosphatases. Although the precise physiological role of this phosphatase is not yet known, its ability to dephosphorylate a wide variety of phosphoproteins and its broad distribution, as shown by a survey of mouse tissues for its activity, suggest that it may serve an important cellular function.

Identification of the substrate and pseudosubstrate binding sites of phosphorylase kinase gamma-subunit

Using site-directed mutagenesis, we proposed that an autoinhibitory domain(s) is located at the C-terminal region (301-386) of the phosphorylase kinase gamma-subunit (Huang, C.-Y.F., Yuan C.-J., Livanova, N.B., and Graves, D.J. (1993) Mol. Cell. Biochem. 127/128, 7-18). Removal of the putative inhibitory domain(s) by truncation results in the generation of a constitutively active and calmodulin-independent form, gamma 1-300. To probe the structural basis of autoinhibition of gamma-subunit activity, two synthetic peptides, PhK13 (gamma 303-327) and PhK5 (gamma 343-367), corresponding to the two calmodulin-binding regions, were assayed for their ability to inhibit gamma 1-300. Competitive inhibition of gamma 1-300 by PhK13 was found versus phosphorylase b (Ki = 1.8 microM) and noncompetitive inhibition versus ATP. PhK5 showed noncompetitive inhibition with respect to both phosphorylase b and ATP. Calmodulin released the inhibition caused by both peptides. These results indicate that there are two distinct auto-inhibitory domains within the C terminus of the gamma-subunit and that these two domains overlap with the calmodulin-binding regions. Two mutant forms of gamma 1-300, E111K and E154R, were used to probe the enzyme-substrate-binding region using peptide substrate analogs corresponding to residues 9-18 of phosphorylase b (KRK11Q12ISVRGL). The data suggest that Glu111 interacts with the P-3 position of the substrate (Lys11) and Glu154 interacts with the P-2 site (Gln12). Both E111K and E154R were competitively inhibited with respect to phosphorylase b by PhK13, with 14- and 8-fold higher Ki values, respectively, than that observed with the wild-type enzyme. These data are consistent with a model for the regulation of the gamma-subunit of phosphorylase kinase in which PhK13 acts as a competitive pseudosubstrate that directly binds the substrate binding site of the gamma-subunit (Glu111 and Glu154).

Increased 8-hydroxydeoxyguanosine in hepatic DNA of rats treated with the peroxisome proliferators ciprofibrate and perfluorodecanoic acid

In this study we examined the ability of peroxisome proliferators to induce oxidative DNA damage in the form of 8-hydroxydeoxyguanosine (OHdG). We studied the hypolipidemic drug ciprofibrate, which is among the most potent and efficacious of the peroxisome proliferators, and perfluorodecanoic acid (PFDA), which is an inhibitor of peroxisomal beta-oxidation. Rats were fed 0.01% ciprofibrate in the diet, or were injected with PFDA at doses of 3 or 10 mg/kg every 14 days (controls and ciprofibrate-fed rats were given equivalent doses of corn oil). Rats were maintained for 10 days, 24 days, 6 weeks, 26 weeks, or 54 weeks. DNA was isolated from the liver at these times and hydrolysed to nucleosides, and the levels of OHdG as well as normal nucleosides were analysed by high-performance liquid chromatography with electrochemical detection. Ciprofibrate increased OHdG concentrations at all times except for the initial 10-day timepoint. Both doses of PFDA increased OHdG levels at all times except the last timepoint, at which only the higher dose produced a significant increase. This study shows that both ciprofibrate and PFDA induce oxidative DNA damage in the form of OHdG. Furthermore, the inhibition of peroxisomal beta-oxidation by PFDA does not affect the development of OHdG.

Effect of the peroxisome proliferators ciprofibrate and perfluorodecanoic acid on hepatic cell proliferation and toxicity in Sprague-Dawley rats

The objective of this study was to compare the effects of perfluorodecanoic acid (PFDA) and ciprofibrate on the induction of hepatic toxicity and on hepatocellular proliferation in rats. In the first study, rats were first subjected to partial hepatectomy and then injected with [3H]thymidine (20 microCi/injection) at 23, 24, 25, 47, 48 and 49 h afterwards. After a 2 week recovery period, rats were injected with one of four levels of PFDA (0.3, 1.0, 3.0 or 10 mg/kg/injection) in four i.p. doses every 14 days, or were fed 0.01% or 0.003% ciprofibrate. Six days after the last PFDA injection and three days before the animals were killed, an osmotic minipump containing 20 mg/ml 5-bromo-2'-deoxyuridine (BrdU) was implanted s.c. for the measurement of DNA synthesis. Peroxisomal fatty acyl-CoA oxidase activity was significantly enhanced in both PFDA and ciprofibrate-treated groups in a dose-dependent manner. Hepatotoxicity, measured as the loss of [3H]thymidine from hepatic DNA, was not significantly affected by any of the treatments. Hepatic DNA synthesis was significantly increased only in rats receiving the highest dose of PFDA. In order to determine the time course of ciprofibrate- and PFDA-induced cell proliferation, we conducted another study with more time points. Rats were fed 0.01% ciprofibrate or were injected every 14 days with 3 or 10 mg PFDA/kg body weight for 10 days, 24 days, 6 weeks, 26 weeks or 54 weeks. Cell proliferation was quantified as in the first study. Ciprofibrate increased cell proliferation at the early but not the later time points, whereas PFDA increased cell proliferation at most times throughout the study. This study demonstrates that PFDA and ciprofibrate do not selectively induce hepatic toxicity and that their effects on cell proliferation do not correlate with their carcinogenic or promoting activities.

Synthetic and oxidative studies on 8-(arylamino)-2'-deoxyguanosine and -guanosine derivatives

Facile aerial oxidation is a general feature of guanine ribo- and 2'-deoxyribonucleosides that are substituted at the 8-position by an aminoaryl group. In previous work, it had been suggested that two of the major oxidation products are a pair of diastereomers having a spiro structure. These were presumed to be related by a chiral difference at the spiro carbon atom. The pattern of the oxidative process involves a contraction of the pyrimidine ring. It was thought to be analogous to that suggested by other investigators for the oxidation of uric acid, but for which no really definitive evidence had been presented. We have been able now to isolate in a crystalline state one of the diastereomers produced by the aerial oxidation of 8-phenylaminoguanosine under alkaline conditions. Analysis by X-ray diffraction has now confirmed the type of spiro structure promulgated previously. These findings also imply that spiro compounds are likely to be produced during the aerial oxidation of any 8-arylaminoguanine nucleoside or 2'-deoxynucleoside. In addition, this work adds considerable weight to the results of Poje and Sokolic-Maravic who proposed that a spiro intermediate is produced during the aerial oxidation of uric acid (12,13). However, they found this compound to be unstable to base, in contrast to the arylaminoguanine oxidation products. In the course of the above work we showed that the 8-arylamino derivatives of guanosine can be converted by the Barton deoxygenation method to the corresponding 2'-deoxyribonucleosides. This makes available a number of the latter compounds, which are not easily prepared by other methods.

Oxidation and site-directed mutagenesis of the sulfhydryl groups of a truncated gamma catalytic subunit of phosphorylase kinase. Functional and structural effects

A truncated form of the gamma subunit of phosphorylase kinase is inactivated by Cu2+ with the formation of two intra-molecular disulfide bonds. The formation of a disulfide bond between Cys-36 and Cys-172 (semioxidized form) results in approximately 50% loss of specific activity because the Km for MgATP is about 10-fold higher. The second disulfide bond is between Cys-184 and Cys-197 and causes further loss of activity. Eight Cys mutants, i.e. C36S, C36A, C42S, C138S, C172S, C184S, C184A, and C197S, were expressed and purified. Kinetic studies suggest that Cys-36 is important for interaction at the nucleotide site because of its hydrophobicity. With Cys-184 mutants, C184S and C184A, tyrosyl phosphorylation of angiotensin II is affected much more than serine kinase activity. The loss of tyrosine kinase activity is related to a lowered activity with Mn2+. With Mn2+, angiotensin II is a competitive inhibitor with respect to seryl kinase activity of C184S. With Mg2+, however, angiotensin II is a noncompetitive inhibitor. We suggest that metal ions influence the conformation of truncated gamma and that the protein substrate binding region containing Cys-184 is important for the dual specificity of this kinase.

Characterization of two novel filamentous phages of Xanthomonas

Two filamentous phages of Xanthomonas campestris pv. vesicatoria and Xanthomonas oryzae pv. oryzae were isolated and designated phi Xv and phi Xo, respectively. They were similar to other filamentous phages of Xanthomonas in (i) shape, (ii) restrictive host specificity, (iii) high stability, (iv) an ssDNA genome, (v) a dsDNA as the replicative form (RF), (vi) propagation without lysis of host cells and (vii) ability to integrate into the host chromosome. These phages showed sequence homology to filamentous phage phi Lf of X. c. pv. campestris. phi Xv was inactivated by antisera against phi Xv, phi Xo and phi Lf, whereas phi Xo and phi Lf were inactivated only by their respective antisera and the anti-phi Xv serum. Both the single-stranded phage DNAs and the RF DNAs of phi Xv, phi Xo and phi Lf were able to transfect X. c. pv. vesicatoria, X. o. pv. oryzae and X. c. pv. campestris. Physical maps of phi Xv and phi Xo were constructed for the RF DNAs. Genome sizes were estimated, based on mapping data, to be 6.8 kb for phi Xv and 7.6 kb for phi Xo, larger than that of the phi Lf genome (6.0 kb). The difference in genome sizes appeared to result from insertions of large DNA fragments. These fragments and the regions mediating integration were localized in the physical maps.

Mutational analyses of the metal ion and substrate binding sites of phosphorylase kinase gamma subunit

Phosphorylase kinase (PhK) and truncated gamma subunit, denoted gamma 1-300, can phosphorylate seryl and tyrosyl residues dependent on the metal ion [Yuan, C.-J., Huang, C. F., & Graves, D. J. (1993) J. Biol. Chem. 268, 17683-17686]. Recombinant gamma 1-300 was used to explore its dual specificity and the location of the metal ion binding sites by using site-directed mutagenesis. Two approaches were taken to generate 26 mutants. First, on the basis of the crystal structure of cAMP-dependent protein kinase (cAPK), the invariant Asn155 and highly conserved Asp168-Phe169-Gly170 residues were mutated. Changes included production of N155H, D168E, D168N, F169R, G170V, G170I, G170L (less than 1% of enzymatic activities were found in these mutants), F169W, and G170A mutants. Second, charge to alanine and charge reversal scanning mutations were used to probe the metal ion binding sites. Two mutants, E111K and E154R, showed very different metal ion response compared to wild-type gamma and were further characterized. The mutants F169W, G170A, E111K, and E154R had 15%, 5%, 8%, and 25% specific activity relative to wild-type gamma, respectively. The folding pattern of wild-type and mutated enzyme forms of gamma was determined by photoacoustic infrared spectroscopy. Conformational disruptions were found in G170V, G170I, and G170L mutants, but the conformation of the rest of the mutants was similar to that of wild-type gamma, suggesting that the loss of enzymatic activities of these mutants was not because of incorrect refolding.(ABSTRACT TRUNCATED AT 250 WORDS)

A study of protein secondary structure by Fourier transform infrared/photoacoustic spectroscopy and its application for recombinant proteins

FT-IR/PAS (Fourier transform infrared/photoacoustic spectroscopy) was used to evaluate the secondary structure of proteins. Four well-studied proteins, concanavalin A, hemoglobin, lysozyme, and trypsin, which have different distributions of secondary structures, were used for assignments of the infrared bands and evaluating the accuracy of FT-IR/PAS methods. Secondary structure contents estimated from FT-IR/PAS and other physical methods (e.g., X-ray diffraction, CD, and traditional FT-IR) show good agreement. In addition, the secondary structure can be evaluated with as little as 0.5 micrograms of protein (concanavalin A), suggesting that FT-IR/PAS is a sensitive and useful technique that could be applied to studies of the folding of recombinant and mutant proteins where only small amounts of material are available. Recombinant phosphorylase kinase gamma 1-300 subunit expressed in Escherichia coli was found in the inclusion bodies. We found that renatured phosphorylase kinase gamma 1-300 subunit has two kinase forms: one has a 10-fold higher activity than the other one. Both fractions, however, are the same as judged from sodium dodecylsulfate-polyacrylamide gel electrophoresis. Differences in conformation were demonstrated by using the FT-IR/PAS method, which showed that the low-activity form has more beta-sheet structure than the form with high activity. Analysis of these kinase forms by CD confirms the interpretation made by the FT-IR/PAS method.

Expression, purification, characterization, and deletion mutations of phosphorylase kinase gamma subunit: identification of an inhibitory domain in the gamma subunit

A catalytic fragment, gamma 1-298, derived from limited chymotryptic digestion of phosphorylase b kinase (Harris, W.R. et al., J. Biol. Chem., 265: 11740-11745, 1990), is reported to have about six-fold greater specific activity than does the gamma subunit-calmodulin complex. To test whether there is an inhibitory domain located outside the catalytic core of the gamma subunit, full-length wild-type and seven truncated forms of gamma were expressed in E. coli. Recombinant proteins accumulate in the inclusion bodies and can be isolated, solubilized, renatured, and purified further by ammonium sulfate precipitation and Q-Sepharose column. Four out of seven truncated mutants show similar (gamma 1-353 and gamma 1-341) or less (gamma 1-331 and gamma 1-276) specific activity than does the full-length wild-type gamma, gamma 1-386. Three truncated forms, gamma 1-316, gamma 1-300, and gamma 1-290 have molar specific activities approximately twice as great as those of the full-length wild-type gamma and the nonactivated holoenzyme. All recombinant gamma s exhibit similar Km values for both substrates, i.e., about 18 microM for phosphorylase b and about 75 microM for MgATP. Three truncated gamma s, gamma 1-316, gamma 1-300, and gamma 1-290, have a 1.9- to 2.5-fold greater catalytic efficiency (Vmax/Km) than that of the full-length wild-type gamma and a 3.5- to 4.5-fold greater efficiency than that of the truncated gamma 1-331. This evidence suggests that there is at least one inhibitory domain in the C-terminal region of gamma, which is located at gamma 301-331. gamma 1-290, but not gamma 1-276, which contains the highly conserved kinase domain, is the minimum sequence required for the gamma subunit to exhibit phosphotransferase activity. Both gamma 1-290 and gamma 1-300 have several properties similar to full-length wild-type gamma, including metal ion responses (activation by free Mg2+ and inhibition by free Mn2+), pH dependency, and substrate specificities.

Effects of chronic alcohol feeding and murine AIDS virus infection on liver antioxidant defense systems in mice

Whether ethanol (ETOH) abuse could contribute to the development of acquired immunodeficiency syndrome (AIDS) among human immunodeficiency virus (HIV)-positive drug abusers is a critical question for which little experimental information is available. This study was designed to determine if chronic ETOH feeding and murine AIDS virus infection cooperatively affected liver antioxidant defense systems in C57B1/6 female mice. Mice were divided into two groups and fed the Lieber-DeCarli liquid ETOH diet containing ETOH at a concentration to provide 31% of total caloric intake or an isocaloric liquid control (control) diet in which dextrin-maltose replaced ETOH. One week after the initiation of ETOH feeding, half of the mice in each diet group (8 mice) were injected intraperitoneally with murine retrovirus (MAIDS) stock. After 3 and 5 weeks of ETOH feeding, half of the mice in each of the four treatment groups (4 mice) were killed, and livers were excised for biochemical analysis. Liver reduced glutathione (GSH) levels and activities of glutathione peroxidase (GP), glutathione reductase (GR), glutathione transferase (GT), catalase and superoxide dismutase (SOD), and serum ETOH concentrations were determined. The results demonstrated that serum ETOH concentrations were significantly elevated in ETOH-MAIDS group when compared with the ETOH group. Moreover, chronic ETOH feeding and MAIDS infection independently depressed liver antioxidant defense capability, and together led to an additive inhibition of GSH and SOD activities. In addition, MAIDS infection inhibited an ETOH-induced increase in catalase and GT activities. These results suggest that alcohol abuse could contribute to the development of AIDS by inhibiting the protective capability of an infected individual against oxidative stress.(ABSTRACT TRUNCATED AT 250 WORDS)

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.