Kinetic study of the inactivation of ascorbate peroxidase by hydrogen peroxide

The activity of ascorbate peroxidase (APX) has been studied with H(2)O(2) and various reducing substrates. The activity decreased in the order pyrogallol>ascorbate>guaiacol>2, 2'-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS). The inactivation of APX with H(2)O(2) as the sole substrate was studied. The number of H(2)O(2) molecules required for maximal inactivation of the enzyme was determined as approx. 2.5. Enzymic activity of approx. 20% of the original remained at the end of the inactivation process (i.e. approx. 20% resistance) when ascorbate or ABTS was used as the substrate in activity assays. With pyrogallol or guaiacol no resistance was seen. Inactivation by H(2)O(2) followed over time with ascorbate or pyrogallol assays exhibited single-exponential decreases in enzymic activity. Hyperbolic saturation kinetics were observed in both assay systems; a similar dissociation constant (0.8 microM) for H(2)O(2) was obtained in each case. However, the maximum rate constant (lambda(max)) obtained from the plots differed depending on the assay substrate. The presence of reducing substrate in addition to H(2)O(2) partly or completely protected the enzyme from inactivation, depending on how many molar equivalents of reducing substrate were added. An oxygen electrode system has been used to confirm that APX does not exhibit a catalase-like oxygen-releasing reaction. A kinetic model was developed to interpret the experimental results; both the results and the model are compared and contrasted with previously obtained results for horseradish peroxidase C. The kinetic model has led us to the conclusion that the inactivation of APX by H(2)O(2) represents an unusual situation in which no enzyme turnover occurs but there is a partition of the enzyme between two forms, one inactive and the other with activity towards reducing substrates such as ascorbate and ABTS only. The partition ratio is less than 1.

Pharmacokinetic evaluation of triiodothyronine supplementation in children after modified Fontan procedure

BACKGROUND

Triiodothyronine (T(3)) supplementation may be a useful adjunct in the management of patients after cardiopulmonary bypass. Limited data are available regarding the use and pharmacokinetics of T(3) in children. The present study was performed to evaluate T(3) pharmacokinetics in a cohort of children undergoing the modified Fontan procedure.

METHODS AND RESULTS

A total of 28 patients were enrolled in this randomized, prospective study. The patients were divided into 4 groups: 1 group received a placebo and 3 groups received intravenous T(3) at dosages of 0.4, 0.6, and 0.8 microg/kg, respectively. All 28 patients survived their operative procedures. Two patients developed low cardiac output, and 3 patients had pleural effusions. The median length of hospital stay was 7 days. The mean free T(3) level was 316+/-67 pg/dL after then administration of a placebo. Patients who received T(3) had mean peak free T(3) levels of 972+/-88, 1351+/-299, and 1869+/-281 pg/dL for the dosages of 0.4, 0.6, and 0.8 microg/kg, respectively. The calculated half-life of T(3) was 7 hours.

CONCLUSIONS

The half-life of intravenous T(3) in children is approximately one-third of that reported for adults. These results provide a framework for studying the efficacy of T(3) supplementation in children undergoing open-heart surgery.

Characterization of isoperoxidase-B2 inactivation in etiolated Lupinus albus hypocotyls

One basic peroxidase isoenzyme, with a pI of 8.8, is present in the intercellular washing fluid in the aerial part of 6-day-old Lupinus albus hypocotyl seedlings. This isoenzyme, called LuP-B2, is the principal soluble component secreted into the apoplastic space and it is a constitutive enzyme along the whole length of etiolated hypocotyl. The enzymatic inactivation process which this apoplastic peroxidase undergoes is described for the first time. The kinetic constants which describe its inactivation by H(2)O(2) in the absence of reductant substrates are determined. LuP-B2 is inactivated in situ and in vitro in a time- and concentration-dependent manner. H(2)O(2) acts as a suicide substrate according to a model previously proposed by us. The constant values calculated are similar to those calculated for the basic isoenzyme of horseradish roots, HRP-C. LuP-B2 presents a k(inact) value of 7.5 x 10(-3) s(-1) and a k(cat) of 6.7 s(-1). This isoenzyme makes 889 catalytic cycles for each inactivation event. The similarity in behavior and the constant values, together with other situations (both are excreted, soluble and constitutive isoenzymes) suggest that the inactivation process could play an important role in plant development and stress situations.

Regulation of a senescence checkpoint response by the E2F1 transcription factor and p14(ARF) tumor suppressor

Normal cells do not divide indefinitely due to a process known as replicative senescence. Human cells arrest growth with a senescent phenotype when they acquire one or more critically short telomeres as a consequence of cell division. Recent evidence suggests that certain types of DNA damage, chromatin remodeling, and oncogenic forms of Ras or Raf can also elicit a senescence response. We show here that E2F1, a multifunctional transcription factor that binds the retinoblastoma (pRb) tumor suppressor and that can either promote or suppress tumorigenesis, induces a senescent phenotype when overexpressed in normal human fibroblasts. Normal human cells stably arrested proliferation and expressed several markers of replicative senescence in response to E2F1. This activity of E2F1 was independent of its pRb binding activity but dependent on its ability to stimulate gene expression. The E2F1 target gene critical for the senescence response appeared to be the p14(ARF) tumor suppressor. Replicatively senescent human fibroblasts overexpressed p14(ARF), and ectopic expression of p14(ARF) in presenescent cells induced a phenotype similar to that induced by E2F1. Consistent with a critical role for p14(ARF), cells with compromised p53 function were immune to senescence induction by E2F1, as were cells deficient in p14(ARF). Our findings support the idea that the senescence response is a critical tumor-suppressive mechanism, provide an explanation for the apparently paradoxical roles of E2F1 in oncogenesis, and identify p14(ARF) as a potentially important mediator of the senescent phenotype.

Influence of 2,3,5-Triiodobenzoic Acid and 1-N-Naphthylphthalamic Acid on Indoleacetic Acid Transport in Carnation Cuttings: Relationship with Rooting

(3)H-IAA transport in excised sections of carnation cuttings was studied by using two receiver systems for recovery of transported radioactivity: agar blocks (A) and wells containing a buffer solution (B). When receivers were periodically renewed, transport continued for up to 8 h and ceased before 24 h. If receivers were not renewed, IAA transport decreased drastically due to immobilization in the base of the sections. TIBA was as effective as NPA in inhibiting the basipetal transport irrespective of the application site (the basal or the apical side of sections). The polarity of IAA transport was determined by measuring the polar ratio (basipetal/acropetal) and the inhibition caused by TIBA or NPA. The polar ratio varied with receiver, whereas the inhibition by TIBA or NPA was similar. Distribution of immobilized radioactivity along the sections after a transport period of 24 h showed that the application of TIBA to the apical side or NPA to the basal side of sections, increased the radioactivity in zones further from the application site, which agrees with a basipetal and acropetal movement of TIBA and NPA, respectively. The existence of a slow acropetal movement of the inhibitor was confirmed by using (3)H-NPA. From the results obtained, a methodological approach is proposed to measure the variations in polar auxin transport. This method was used to investigate whether the variations in rooting observed during the cold storage of cuttings might be related to changes in polar auxin transport. As the storage period increased, a decrease in intensity and polarity of auxin transport occurred, which was accompanied by a delay in the formation and growth of adventitious roots, confirming the involvement of polar auxin transport in supplying the auxin for rooting.

Methods to measure the antioxidant activity in plant material. A comparative discussion

Methods to determine total antioxidant activity (TAA) are generally based on the inhibition of certain reactions by the presence of antioxidants. The most widely used methods are those that involve the generation of radical compounds, and it is the presence of antioxidants that determines the disappearance of these radicals. Strategies for measuring TAA are discussed, particularly the different methodological and instrumental approaches used. In addition, our own methods are presented in order to facilitate and speed up the manipulation of biological material. The values of TAA by different compounds are presented and compared.

Development of a serologic assay to detect Taenia solium taeniasis

We developed a serologic assay to identify adult Taenia solium tapeworm carriers using excretory/secretory (TSES) antigens collected from in vitro cultured T. solium tapeworms. To identify taeniasis-specific antigens we used an immunoblot assay with serum samples from T. solium tapeworm carriers and cysticercosis patients. Antigens were identified that reacted with antibodies present in serum samples from taeniasis cases and not with those from cysticercosis patients. Using serum samples collected from persons with confirmed T. solium tapeworm infections, the test was determined to be 95% (69 of 73) sensitive. Serum samples (n = 193) from persons with other parasitic infections, including T. saginata tapeworm infections, do not contain cross-reacting antibodies to TSES, indicating that the assay is 100% specific. These data suggest that the immunoblot assay using TSES antigens can be used to identify persons with current or recent T. solium tapeworm infections and provides a new, important tool for epidemiologic purposes, including control and prevention strategies.

Molecular analysis of H2O2-induced senescent-like growth arrest in normal human fibroblasts: p53 and Rb control G1 arrest but not cell replication

Human diploid fibroblasts lose the capacity to proliferate and enter a state termed replicative senescence after a finite number of cell divisions in culture. When treated with sub-lethal concentrations of H2O2, pre-senescent human fibroblasts enter long-term growth arrest resembling replicative senescence. To understand the molecular basis for the H2O2-induced growth arrest, we determined the cell cycle distribution, levels of p53 tumour suppressor and p21 cyclin-dependent kinase inhibitor proteins, and the status of Rb phosphorylation in H2O2-treated cells. A 2-h pulse of H2O2 arrested the growth of IMR-90 fetal lung fibroblasts for at least 15 days. The arrested cells showed a G1 DNA content. The level of p53 protein increased 2- to 3-fold within 1.5 h after H2O2 exposure but returned to the control level by 48 h. The induction of p53 protein was dose dependent, beginning at 50-75 microM and reaching a maximum at 100-250 microM. The induction of p53 did not appear to correlate with the level of DNA damage as measured by the formation of 8-oxo-2'-deoxyguanosine in DNA. The level of p21 protein increased about 18 h after H2O2 exposure and remained elevated for at least 21 days. During this period, Rb remained underphosphorylated. The induction of p53 by H2O2 was abolished by the iron chelator deferoxamine and the protein synthesis inhibitor cycloheximide. The human papillomavirus protein E6, when introduced into the cells, abolished the induction of p53, reduced the induction of p21 to a minimal level and allowed Rb phosphorylation and entry of the cells into S-phase. The human papillomavirus protein E7 reduced the overall level of Rb and also abolished H2O2-induced G1 arrest. Inactivating G1 arrest by E6, E7 or both did not restore the replicative ability of H2O2-treated cells. Thus H2O2-treated cells show a transient elevation of p53, high level of p21, lack of Rb phosphorylation, G1 arrest and inability to replicate when G1 arrest is inactivated.

The inactivation and catalytic pathways of horseradish peroxidase with m-chloroperoxybenzoic acid. A spectrophotometric and transient kinetic study

The kinetics of the catalytic cycle and irreversible inactivation of horseradish peroxidase C (HRP-C) reacting with m-chloroperoxybenzoic acid (mCPBA) have been studied by conventional and stopped-flow spectrophotometry. mCPBA oxidized HRP-C to compound I with a second order-rate constant k1 = 3.6 x 10(7) M-1 s-1 at pH 7.0, 25 degrees C. Excess mCPBA subsequently acted as a one-electron reducing substrate, converting compound I to compound II and compound II to resting, ferric enzyme. In both of these reactions, spectrally distinct, transient forms of the enzyme were observed (lambdamax = 411 nm, epsilon = 45 mM-1 cm-1 for compound I with mCPBA, and lambdamax = 408 nm, epsilon = 77 mM-1 cm-1 for compound II with mCPBA). The compound I-mCPBA intermediate (shown by near infrared spectroscopy to be identical to P965) decayed either to compound II in a catalytic cycle (k3 = 6.4 x 10(-3) s-1) or, in a competing inactivation reaction, to verdohemoprotein (ki = 3.3 x 10(-3) s-1). Thus, a partition ratio of r = 2 is obtained for the inactivation of ferric HRP-C by mCPBA. The intermediate formed from compound II with mCPBA is not part of the inactivation pathway and only decays via the catalytic cycle to give resting, ferric enzyme (k5 = 1.0 x 10(-3) s-1). The data are compared with those from earlier steady-state kinetic studies and demonstrate the importance of single turnover experiments. The results are discussed in terms of the physiologically relevant reactions of plant peroxidases with hydrogen peroxide.

Nursing staff time allocation in long-term care: a work sampling study

The effective use of nursing staff time is a major determinant of the quality of care in long-term care facilities. The purpose of this work sampling study was to identify those activities that consumed the largest amount of staff time on a locked unit housing: 60 chronically ill and demented patients. A heavy work load, large proportion of direct care, and minimal nonproductive time were found. Work redesign strategies to improve staff efficiency and implications for further research are discussed.

Indole-3-carbinol as a scavenger of free radicals

The ability of indole-3-carbinol (indole-3-methanol) to trap a metastable synthetic-free radical is presented. Indole-3-carbinol is capable of acting as a scavenger of free radicals in an in vitro system. The presence of indole-3-carbinol determines the disappearance of the free radicals, the reaction being time- and concentration-dependent. The scavenging activity of different indoles is compared. Indole-3-carbinol and indole-3-acetic acid are both able to scavenge free radicals, but indole-3-carbinol is more effective. Other indoles such as indole-3-aldehyde and indole-3-carboxylic acid do not show the ability to trap free radicals. Indole-3-aldehyde appears as a product of indole-3-carbinol reaction with free radicals. The formation of an adduct between the free radical generated in vitro and indole-3-carbinol has also been detected. Stability of indole-3-carbinol in buffered media at different pH values and formation of 3,3'-diindolylmethane from indole-3-carbinol is also studied. The scavenging activity of indole-3-carbinol and its implications on the anti-carcinogenesis process is discussed.

Epidural hematoma after epidural anesthesia in a patient with peripheral vascular disease. Case report

BACKGROUND AND OBJECTIVES

Epidural hematoma is a severe, uncommon complication associated with epidural anesthesia in patients with peripheral vascular disease who require anticoagulant therapy.

METHODS

An 84-year-old woman with acute left leg arterial ischemia underwent revascularization surgery under lumbar epidural anesthesia. Pre- and postoperative heparin was administered as an anticoagulant.

RESULTS

Reperfusion of the leg was successful, however, 3 days later clinical signs of spinal cord compression appeared and epidural hematoma was diagnosed. Neurologic recovery was poor.

CONCLUSIONS

This case highlights the need for careful individual preoperative analysis and postoperative observation to make anesthetic practice safe in patients receiving perioperative anticoagulant therapy.

Role of the reductant substrates on the inactivation of horseradish peroxidase by m-chloroperoxybenzoic acid

Horseradish peroxidase reacts with H2O2 and other hydroperoxides to form Compound I, the first active enzymatic form m-Chloroperoxybenzoic acid, a xenobiotic hydroperoxide, acts as an oxidant substrate of horseradish peroxidase. However, this hydroperoxide is also a powerful inactivator of the enzyme and in this sense is more effective than H2O2. The coupled reductant substrates used in the peroxidatic reaction protect the enzyme from the inactivating process. A reaction mechanism is proposed with two competitive routes: one catalytic and one inactivating. Using a kinetic approach, the ratio between the hydroperoxide and the reductant substrate appears to be a decisive factor in the catalytic turnover of the enzyme. The role of the reductant substrates in protecting the enzyme, and the physiological and biotechnological implications of this process are discussed.

Replicative senescence, aging and growth-regulatory transcription factors

Normal somatic cells invariably enter a state of permanent growth arrest and altered function after a finite number of divisions. This phenomenon is termed cellular or replicative senescence. Replicative senescence is thought to be a tumor-suppressive mechanism, and a contributing factor in aging. Three features distinguish senescent from presenescent cells: an irreversible block to cell proliferation, increased resistance to apoptotic death, and changes in differentiated functions. Senescence entails an altered pattern of gene expression, much of which is due to altered transcription. At least three growth regulatory transcriptional modulators are repressed in senescent cells: the c-fos component of the AP1 transcription factor, the Id1 and Id2 helix-loop-helix (HLH) proteins that negatively regulate basic HLH transcription factors, and the E2F-1 component of the E2F transcription factor. Failure to express any one of these modulators is very likely sufficient to arrest cell proliferation. Loss of these modulators may also explain many of the functional changes shown by senescent cells. In the case of c-fos repression, the resulting decline in AP-1 activity may be exacerbated by an altered ratio of AP-1 components to a protein known as QM or Jif. QM interacts with the c-jun component of AP-1 and suppresses AP-1 activity. We cloned QM from a senescent fibroblast cDNA library, and found that it was neither cell cycle- nor senescence-regulated. However, QM suppressed the growth of murine and human fibroblasts when overexpressed. Thus, an altered balance between positive factors (e.g., AP-1 components) and negative factors (e.g., QM) may lead to the growth arrest, as well as the changes in differentiated gene expression, that are a hallmark of senescent cells.

Inhibition by L-ascorbic acid and other antioxidants of the 2.2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) oxidation catalyzed by peroxidase: a new approach for determining total antioxidant status of foods

The accumulation of 2.2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical catalyzed by peroxidase can be inhibited by the presence of L-ascorbic acid in the reaction medium, this inhibition delaying the accumulation of the ABTS radical and giving rise to a lag time. A kinetic approach to explain this lag time is presented, which also makes it possible to determine the amount of L-ascorbic acid in the reaction medium. The stoichiometry of the system was determined as 1 mol of L-ascorbic reducing 2 mol of ABTS radicals. L-Ascorbic acid is not the only compound to have this ability, since other antioxidant compounds also react with the ABTS radical. We studied the ABTS/H2O2/horseradish peroxidase system in the presence of L-ascorbic acid and other antioxidant compounds. The influence of such factors as pH, enzyme concentration, and L-ascorbic acid concentration was studied. A good correlation between the lag time and the L-ascorbic acid present in the medium was observed, and under optimal conditions, the method could determine as little as 0.65 nmol of L-ascorbic acid. Based on our findings, we propose a method to measure the total antioxidant activity of different compounds related to L-ascorbic acid and apply this method to determining the total antioxidant activity present in fruit juices.

A comparative study of the inactivation of wild-type, recombinant and two mutant horseradish peroxidase isoenzymes C by hydrogen peroxide and m-chloroperoxybenzoic acid

The mechanism-based inactivation of four horseradish peroxidase (HRP-C) enzyme variants has been studied kinetically with either hydrogen peroxide or the xenobiotic m-chloroperoxybenzoic acid (mClO2-BzOH) as sole substrate. The concentration and time dependence of inactivation was investigated for the wild-type plant enzyme (HRP-C), the unglycosylated recombinant enzyme (HRP-C*), and two site-directed mutants with Phe143 replaced by Ala ([F143A]HRP-C*) or Arg38 replaced by Lys ([R38K]HRP-C*). The number of turnovers (r) of H2O2 required to completely inactivate the enzymes was found to vary between the different enzymes with HRP-C being most resistant to inactivation (r = 625), HRP-C* and [F143A]HRP-C* being approximately twice as sensitive (r = 335 and 385, respectively) in comparison, and [R38K]HRP-C* being inactivated much more easily (r = 20). In the cases of HRP-C* and [F143A]HRP-C*, compared to HRP-C the differences were due to the absence of glycosylation on the exterior of the proteins, whilst the [R38K]HRP-C* variant exhibited a distinct mechanistic difference. When mClO2BzOH was used as the substrate the differences in sensitivity to inactivation disappeared. The values of r were all around 3 reflecting the strong affinity of mClO2BzOH for the active site. The apparent rate constant for inactivation by H2O2 was found to be about twofold higher in [R38K]HRP-C* than the other enzymes and the catalytic constant for turnover of H2O2 was approximately ten times lower. The affinity of compound I for H2O2 leading to the formation of a transitory intermediate implicated in the inactivation of peroxidase decreased in the order HRP-C, HRP-C*, [F143A]HRP-C*, [R38K]HRP-C*.

A biomarker that identifies senescent human cells in culture and in aging skin in vivo

Normal somatic cells invariably enter a state of irreversibly arrested growth and altered function after a finite number of divisions. This process, termed replicative senescence, is thought to be a tumor-suppressive mechanism and an underlying cause of aging. There is ample evidence that escape from senescence, or immortality, is important for malignant transformation. By contrast, the role of replicative senescence in organismic aging is controversial. Studies on cells cultured from donors of different ages, genetic backgrounds, or species suggest that senescence occurs in vivo and that organismic lifespan and cell replicative lifespan are under common genetic control. However, senescent cells cannot be distinguished from quiescent or terminally differentiated cells in tissues. Thus, evidence that senescent cells exist and accumulate with age in vivo is lacking. We show that several human cells express a beta-galactosidase, histochemically detectable at pH 6, upon senescence in culture. This marker was expressed by senescent, but not presenescent, fibroblasts and keratinocytes but was absent from quiescent fibroblasts and terminally differentiated keratinocytes. It was also absent from immortal cells but was induced by genetic manipulations that reversed immortality. In skin samples from human donors of different age, there was an age-dependent increase in this marker in dermal fibroblasts and epidermal keratinocytes. This marker provides in situ evidence that senescent cells may exist and accumulate with age in vivo.

Clinical performance of the TCu 380A and Lippes Loop IUDs in three developing countries

The clinical performance of the Copper T 380A (TCu 380A) and the Lippes Loop intrauterine devices (IUDs) were evaluated for 12 months in a group of 710 women who had one of the two IUDs inserted. Results are from a randomized clinical trial conducted at three collaborating research sites located in three developing countries. The gross cumulative life-table pregnancy rate of the TCu 380A IUD was found to be lower than that of the Lippes Loop IUD at 12 months (0.7 and 2.1 per women, respectively). Although this difference was not statistically significant (p = 0.25), it is similar to findings from other studies. The 12-month cumulative removal rate due to personal reasons was significantly different (1.4 and 0.0, respectively, p = 0.05). Statistically significant differences between the two study IUDs were not found with regard to IUD expulsion or IUD removal due to bleeding/pain, medical reasons, planned pregnancy or investigator's choice. A statistically significant difference (p = 0.03) was observed in the number of TCu 380A IUD users experiencing dysmenorrhea (26.1%) during the 12-month study period, compared to Lippes Loop IUD users (18.8%).

[Postinfarction ventricular septal defect. Surgical approach by right ventriculotomy in 4 patients]

Ventricular septal defect secondary to myocardial infarction still have high mortality. Early and swift surgical repair is needed to obtain adequate results. Surgical exposure of defect through the infarcted left ventricle wall is the usual technique. Nevertheless right ventricular access to the interventricular septum has given excellent results on 4 of our patients. Our results are analyzed.

A kinetic study of simultaneous suicide inactivation and irreversible inhibition of an enzyme. Application to 1-aminocyclopropane-1-carboxylate (ACC) synthase inactivation by its substrate S-adenosylmethionine

This paper deals with the development of an experimental method for the kinetic study of the inactivation of an enzyme by a racemic mixture of an inhibitor, whose isomers operate as suicide substrate and irreversible inhibitor respectively. The ratio between the isomer concentration in the biological or commercial source must be determined, but no separation of them is required. The method involves a kinetic analysis and an experimental design that enables the affinity (1/Km), rate of catalysis (kcat), rate of inactivation (lambda max), efficiency of catalysis (kcat/Km) and efficiency of inactivation (lambda max/Km) to be determined. The method has been applied to the kinetic characterization of the inactivation of 1-aminocyclopropane-1-carboxylate (ACC) synthase from tomato fruits by its substrate, S-adenosylmethionine (AdoMet). The ratio between AdoMet isomers with respect to its sulfonium centre, namely (-)-AdoMet and (+)-AdoMet, present in the commercial sample used, has been determined by 1H nuclear magnetic resonance.

Catalytic oxidation of 2,4,5-trihydroxyphenylalanine by tyrosinase: identification and evolution of intermediates

The oxidation of 3,4-dihydroxyphenylalanine (dopa) by O2 catalyzed by tyrosinase yields 4-(2-carboxy-2-aminoethyl)-1,2-benzoquinone, with its amino group protonated (o-dopaquinone-H+). This evolves non-enzymatically through two branches (cyclization and/or hydroxylation), whose respective operations are determined by pH. The hydroxylation branch of o-dopaquinone-H+ only operates significantly at pH < or = 5.0 and involves the accumulation of 2,4,5-trihydroxyphenylalanine (topa), which has been detected by high-performance liquid chromatography (HPLC). This last compound is also a substrate of tyrosinase. The oxidation of topa by both tyrosinase and periodate yields 5-(2-carboxy-2-aminoethyl)-4-hydroxy-1,2-benzoquinone, with its amino group protonated (o-topaquinone-H+), which is red (RTQH) (lambda max 272-485 nm) at pH 7.0 and yellow (TTQH) (lambda max 265-390 nm) at pH 3.0. This is based on pKa 4.5 of the 2-OH group of the benzene ring of o-topaquinone-H+, as derived from spectrophotometric and HPLC assays. At physiological pH, RTQH undergoes deprotonation of the ammonium group of the side chain to yields RTQ, which cyclize into 2-carboxy-2,3-dihydroxyindolen-5,6-quinone (dopachrome), with a 1:1 stoichiometry and first-order kinetics. The evolution of RTQH has been analyzed by spectrophotometry, HPLC, cyclic voltammetry and constant potential electrolytic assays. From HPLC assays, the value of the first-order constant for the evolution of RTQH at pH 7.0 (kRTQHapp 4.83 x 10(-5) s-1), as well as of the rate constant for the cyclization step of RTQ (kRTQc 2.53 x 10(-3) s-1) were determined.

The decrease in auxin polar transport down the lupin hypocotyl could produce the indole-3-acetic Acid distribution responsible for the elongation growth pattern

The variation of indole-3-acetic acid (IAA) transport along Lupinus albus L. hypocotyls was studied using decapitated seedlings and excised sections. To confirm that the mobile species was IAA and not IAA metabolites, dual isotope-labeled IAAs, [5-(3)H]IAA + [1-(14)C]IAA, were used. After apical application to decapitated seedlings, the longitudinal distribution of both isotopes at different transport periods showed that the velocity of IAA transport was higher in the apical, elongating region than in the basal, non-growing region. This variation in velocity was not a traumatic consequence of decapitation because after application of IAA to the basal region of decapitated seedlings, both the velocity and intensity of IAA transport were lower than in the apical treatment. The variation in IAA transport down the hypocotyl was confirmed when it was measured in excised sections located at different positions along the hypocotyl. The velocity and, to a greater extent, the intensity of IAA transport decreased from the apical to the basal sections. Consequently, if the amount of IAA reaching the apical zones of lupin hypocotyl were higher than the IAA transport capacity in the basal zones, accumulation of mobile IAA might be expected in zones located above the basal region. In fact, an IAA accumulation occurred in the elongating region during the first 4-h period of transport after apical treatment with IAA. It is proposed that the fall in IAA transport along the hypocotyl might be responsible for the IAA distribution and, consequently, for the growth distribution reported in this organ. An indirect proof of this was obtained from experiments that showed that the excision of the slowly transporting basal zones strongly reduced the growth in the remaining part of the organ, whereas excision of the root caused no significant modification in growth during a 20-h period.

The use of low glycaemic index foods improves metabolic control of diabetic patients over five weeks

The aim of the present study was to determine whether any benefit might occur from lowering the glycaemic index of diet in the medium term in diabetic patients. Eighteen well-controlled diabetic patients (12 Type 1 and 6 Type 2 non-insulin-treated), were assigned to either a high mean glycaemic index or low mean glycaemic index diet for 5 weeks each in a random order using a cross-over design. The two diets were equivalent in terms of nutrient content and total and soluble fibre content. The glycaemic indices were 64 +/- 2 (mean +/- SD) % and 38 +/- 5% for the two diets. The high glycaemic index diet was enriched in bread and potato and the low glycaemic index diet in pasta, rice, and legumes. At the end of the study periods, the following variables were improved on the low compared to the high glycaemic index diet: fructosamine (3.9 +/- 0.9 vs 3.4 +/- 0.4 mmol l-1, p less than 0.05); fasting blood glucose (10.8 +/- 2.8 vs 9.6 +/- 2.7 mmol l-1, p less than 0.02); 2-h postprandial blood glucose (11.6 +/- 2.9 vs 10.3 +/- 2.5 mmol l-1, p less than 0.02); mean daily blood glucose (12.0 +/- 2.5 vs 10.4 +/- 2.7 mmol l-1, p less than 0.02); serum triglycerides (1.5 +/- 0.9 vs 1.2 +/- 0.6 mmol l-1, p less than 0.05). No significant differences were found in body weight, HbA1C, insulin binding to erythrocytes, insulin and drug requirements, and other circulating lipids (cholesterol, HDL-cholesterol, phospholipids, Apolipoprotein A1, Apolipoprotein B). Thus the inclusion of low glycaemic index foods in the diet of diabetic patients may be an additional measure which slightly but favourably influences carbohydrate and lipid metabolism, requires only small changes in nutritional habits and has no known deleterious effects.

Modification by ethylene of the cell growth pattern in different tissues of etiolated lupine hypocotyls

The influence of ethylene on growth in etiolated lupine (Lupinus albus L.) hypocotyls was studied in ethephon-treated plants. Ethephon reduced the length and increased the diameter of hypocotyls. At the end of the hypocotyl growth period (14 days), the fresh weight was reduced by 53%, and the dry weight was reduced by 16%. Thus, ethylene reduced water uptake in the tissues to a greater extent than the incorporation of new materials. Light microscopic measurements showed that the thickness of tissues was stimulated by ethylene, the vascular cylinder and cortex exhibiting greater increases (55 and 45%, respectively) than pith (26%) or epidermis (12%). Ethephon modified the cell growth pattern, stimulating lateral cell expansion and cell wall thickness, while reducing cell elongation. The response to ethylene varied in the different tissues and was higher in cortex and pith cells than in the epidermis cells. The ethylene-induced cell expansion in the cortex varied according to the localization of cells in the tissue: the central and subepidermal layers showed little change, whereas the innermost layers exhibited the greatest increase. Electron microscopy revealed that ethylene increased both the rough endoplasmic reticulum and dictyosomes, suggesting that ethylene stimulated the secretion of cell wall materials. In untreated seedlings, the pattern of cell growth was similar in cells from the epidermis, cortex, and pith. The final cell size varied along the hypocotyl, the cells becoming shorter and broader the closer to the basal zones of the organ.

Lateral diffusion of polarly transported indoleacetic acid and its role in the growth of Lupinus albus L. hypocotyls

The transport and metabolism of indole-3-acetic acid (IAA) was studied in etiolated lupin (Lupinus albus L, cv. Multolupa) hypocotyls, following application of dual-isotope-labelled indole-3-acetic acid, [5-(3)H]IAA plus [1-(14)C]IAA, to decapitated plants. To study the radial distribution of the transported and metabolized IAA, experiments were carried out with plants in which the stele was separated from the cortex by a glass capillary. After local application of labelled IAA to the cortex, radioactivity remained immobilized in the cortex, near the application point, showing that polar transport cannot occur in the outer tissues. However, following application of IAA to the stele, radioactivity appeared in the cortex in those hypocotyl sections below the first 1 cm (in which the capillary was inserted), and the basipetal IAA movement was similar to that observed after application of IAA to the complete cut surface. In both assays, longitudinal distribution of (14)C and (3)H in the stele outside the first 1 cm was positively correlated with that of cortex, indicating that there was a lateral migration of IAA from the transport pathway (in the stele) to the outer tissues and that this migration depended on the amount of IAA in the stele. Both tissues (stele and cortex) exhibited intensive IAA metabolism, decarboxylation being higher in the stele than in the cortex while IAA conjugation was the opposite. Decapitation of the seedlings caused a drastic reduction of hypocotyl growth in the 24 h following decapitation, unless the hypocotyls were treated apically with IAA. Thus, exogenous IAA, polarly transported, was able to substitute the endogenous source of auxin (cotyledons plus meristem) to permit hypocotyl growth. It is proposed that IAA escapes from the transporting cells (in the stele) to the outer tissues in order to reach the growth-responsive cells. The IAA metabolism in the outer tissues could generate the IAA gradient necessary for the maintenance of its lateral flow, and consequently the auxin-induced cell elongation.

[Aortic valve replacement by a pulmonary homograft]

Minor experience still exists in our country with regard to the use of valve homografts in cardiac surgery. Only a few implantations have been performed in cases of right ventricular outflow tract reconstruction in addition to our own experience in cases of infective endocarditis of the aortic valve. We present a case of aortic valve replacement by using an antibiotic-sterilized fresh pulmonary valve autograft. The case is described and the possible advantages of the use of pulmonary allografts in the aortic position are discussed.

Delayed sternal closure for life-threatening complications in cardiac operations: an update

Over a 7-year-period, 25 patients had delayed sternal closure after open heart operations out of 34 patients whose sternum was not closed. The indications were extreme cardiac dilatation and uncontrollable mediastinal hemorrhage. This represented a 1.79% incidence in the overall open heart surgical experience at our unit. Sternal closure was performed at a mean of 2.64 days after the initial operation. Eighteen patients (52.9%) left the hospital alive and well, representing a 72% survival rate among patients undergoing delayed sternal closure. No mediastinal or fatal infection developed and only 1 patient had late superficial wound infection after delayed sternal closure. We conclude that delayed sternal closure is an effective method to treat severe complications after cardiac operations.

1-Aminocyclopropane-1-carboxylic acid as a substrate of peroxidase: conditions for oxygen consumption, hydroperoxide generation and ethylene production

Conditions in which 1-aminocyclopropane-1-carboxylic acid (ACC) functions as a substrate of peroxidase have been investigated by measuring oxygen consumption in the reaction medium and the production of ethylene. In both cases, the presence of Mn2+ and either H2O2 or the activated form of peroxidase, namely compound I of peroxidase, was found to be essential. Both oxygen consumption and ethylene production were dependent on enzyme concentration, the optimum ACC/Mn2+ ratio being 1:1. Oxygen consumption in a system with ACC, Mn2+ and compound I showed an enzyme-dependent lag phase and then proceeded to total depletion, suggesting that the system itself generates hydroperoxides that completed the catalytic cycle of the enzyme. The presence of these hydroperoxides in the reaction medium was detected by a colorimetric method. High H2O2 concentration progressively decreased oxygen consumption, the same effect being produced by catalase. Ethylene production was oxygen dependent, mediated by ACC-free radicals and gave a poor yield. The results suggest that the fate of these ACC-free radicals determines the yield in ethylene. These radicals must be oxidized immediately, otherwise their stabilization to hydroperoxides would prevent ethylene production.

1-Aminocyclopropane-1-carboxylic acid as a substrate of peroxidase: conditions for oxygen consumption, hydroperoxide generation and ethylene production

Conditions in which 1-aminocyclopropane-1-carboxylic acid (ACC) functions as a substrate of peroxidase have been investigated by measuring oxygen consumption in the reaction medium and the production of ethylene. In both cases, the presence of Mn2+ and either H2O2 or the activated form of peroxidase, namely compound I of peroxidase, was found to be essential. Both oxygen consumption and ethylene production were dependent on enzyme concentration, the optimum ACC/Mn2+ ratio being 1:1. Oxygen consumption in a system with ACC, Mn2+ and compound I showed an enzyme-dependent lag phase and then proceeded to total depletion, suggesting that the system itself generates hydroperoxides that completed the catalytic cycle of the enzyme. The presence of these hydroperoxides in the reaction medium was detected by a colorimetric method. High H2O2 concentration progressively decreased oxygen consumption, the same effect being produced by catalase. Ethylene production was oxygen dependent, mediated by ACC-free radicals and gave a poor yield. The results suggest that the fate of these ACC-free radicals determines the yield in ethylene. These radicals must be oxidized immediately, otherwise their stabilization to hydroperoxides would prevent ethylene production.

[Replacement of the aortic root and ascending aorta with a fresh antibiotic-sterilized homograft]

The case of a 53-year-old male suffering from aortic stenosis and aneurysm of the ascending aorta treated by aortic root replacement with a fresh antibiotic-sterilized aortic homograft is presented. The technique and indications are commented on, focusing attention in the scanty results available in the literature with regard to this technique. We support the use of homografts in aortic root replacement in selected cases.

A kinetic study on the suicide inactivation of peroxidase by hydrogen peroxide

In the absence of reductant substrates, and with excess H2O2, peroxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) shows the kinetic behaviour of a suicide inactivation, H2O2 being the suicide substrate. From the complex (compound I-H2O2), a competition is established between two catalytic pathways (the catalase pathway and the compound III-forming pathway), and the suicide inactivation pathway (formation of inactive enzyme). A kinetic analysis of this system allows us to obtain a value for the inactivation constant, ki = (3.92 +/- 0.06) x 10(-3) x s-1. Two partition ratios (r), defined as the number of turnovers given by one mol of enzyme before its inactivation, can be calculated: (a) one for the catalase pathway, rc = 449 +/- 47; (b) the other for the compound III-forming pathway, rCoIII = 2.00 +/- 0.07. Thus, the catalase activity of the enzyme and, also, the protective role of compound III against an H2O2-dependent peroxidase inactivation are both shown to be important.

Is the copper T 380A device associated with an increased risk of removal due to bleeding and/or pain? An analysis

Previous studies have consistently shown that the family of the Copper T 380 devices is more effective in preventing accidental pregnancies than the inert, as well as most other, if not all, copper devices. However, a number of these studies also reported a higher removal rate due to bleeding and/or pain for the TCu 380A than for other devices. The programmatical importance of these findings prompted us to analyze the international multi-center randomized clinical trial datasets to examine this question on the new TCu 380A (ParaGard) recently marketed in the U.S. Our results, while confirming the inherent superior efficacy of the TCu 380A, did not reveal a significantly higher removal rate because of bleeding and/or pain among TCu 380A users than among users of the comparative devices, which included the Lippes Loop D, the TCu 200, the TCu 220 and the Multiload Cu 250 devices.

Inactivation of peroxidase by hydrogen peroxide and its protection by a reductant agent

Hydrogen peroxide, the oxidant substrate of peroxidase, is also an inactivating agent of this enzyme. The reductant substrates protect the enzyme from the inactivating process. A reaction mechanism is proposed, in which two competitive routes exist for Compound I of peroxidase; one catalytic and one inactivating. The analytical solution produced at the end of the reaction supports the proposed mechanism and shows the dependence between the number of turnovers of the enzyme (r) and the ratio of both substrates.

An enzymatic colorimetric method for measuring naringin using 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid)(ABTS) in the presence of peroxidase

A sensitive colorimetric method for naringin estimation using 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) as peroxidase substrate is described. The method is based on the coupling reaction of an ABTS radical cation with an oxidation product of naringin formed by peroxidase. This coupling reaction leads to the formation of a purple-colored compound with a maximum absorption at 560 nm. A molar absorption coefficient at this wavelength was calculated to be 13,286 +/- 200 M-1 cm-1. The lowest amount of naringin that can be detected is 1 nmol. The application of this method to the quantification of naringin in grapefruit tissues is presented.

[Ascending thoracic aorta-supraceliac abdominal aorta by-pass in a patient with coarctation and partial hypoplasia of the arch and aortic isthmus]

A twenty years old patient, with arterial hypertension at the right arm and absent pulse in both lower extremities was studied by angiography, and a coarctation of aortic arch with partial hypoplasia of aortic arch and aortic isthmus was found. Patient underwent to a surgical operation and, by anterior approach, an ascending thoracic aorta-supraceliac abdominal aorta by-pass was made. In the present case report, advantages, indications and experience with such by-pass modality are review.

A new technical alternative in the surgery for retroperitoneal fibrosis: the Gore-Tex surgical membrane

The case of a male patient with retroperitoneal fibrosis secondary to an abdominal aortic aneurysm which was surgically treated with success, is presented herein. What is considered technically new is the management of the ureters after surgical lysis. An expanded polytetrafluoroethylene Gore-Tex surgical membrane, initially developed for pericardial closure after open-heart surgery, was used to isolate the bifurcated aortofemoral graft from the duodenum and the ureters from the vascular prosthesis and surrounding retroperitoneal tissues. This is considered to be a simple and safe technique and a technical alternative when dealing with this complex situation. To date, there has been no other description of such a technique using this material. The potential value of this material to prevent reencasement in retroperitoneal fibrosis from other origins should be kept in mind.

Is glucose self-monitoring beneficial in non-insulin-treated diabetic patients? Results of a randomized comparative trial

To study if self-monitoring of glucose, urinary or capillary, could help them to improve their metabolic control through better compliance to diet and/or hypoglycaemic agents, 208 non-insulin-treated poorly controlled diabetic patients were randomized to: group A--regular HbA1c determinations but no self-monitoring, group B--self-urine glucose monitoring, twice every other day, group C--self blood glucose monitoring, twice every other day, and followed six months. At the end of the study period, the decrease of HbA1c over six months--main endpoint--was not significantly different between the three groups (mean +/- SEM; group A: -0.5 +/- 0.2%; group B: -0.1 +/- 0.3%; group C: -0.4 +/- 0.3%). However, the degree of compliance to blood glucose self-monitoring in group C appeared to relate to the outcome: a significant correlation was found between the number of blood glucose strips used and the decrease of HbA1c (r = .36, p less than .02). We conclude that regular self-monitoring has no definite advantage over the usual management for improving metabolic control in non-insulin-treated diabetic patients, though it may possibly help patients ready to comply with its use.

Oxygen consumption during the indole-3-acetic acid oxidation catalyzed by peroxidase. Effect of the enzyme/substrate ratio

Oxygen consumption during the oxidation of indole-3-acetic acid (IAA) by peroxidase has been studied, in conditions of no limitation by oxygen. For different enzyme/substrate ratios the quotient O2 consumed/IAA oxidized shows rather small differences and it is always less than unity. During the reaction, however, the quotient undergoes important variations because oxygen uptake ceases long before the decarboxylation of IAA. The results are discussed in the light of previous proposed mechanisms.

Effects of enzyme/substrate ratio and of cofactors on the oxidation products of indole-3-acetic acid catalyzed by peroxidase

During the oxidation of indole-3-acetic acid catalyzed by peroxidase, the relative amounts of the products closely depends on the enzyme/substrate ratio. In the absence of cofactors, high enzyme/substrate ratio induces a rise in the level of indole-3-aldehyde and indole-3-methanol, and a drop in that of oxindoles. 2,4-dichlorophenol, although a very efficient cofactor, promotes inhibition of the oxidation after a few minutes, presumably through the formation of a phenol-derivative inhibitor. 2-4-dichlorophenol also inhibits the production of oxindoles at all stages. Both inhibitory effects are abolished by a low concentration of enzyme. Mn2+, itself a weak inhibitor, synergizes the catalytic effect of 2,4-dichlorophenol, perhaps by preventing the formation of the inhibitor. The results are discussed against more widely accepted mechanisms of indole-3-acetic acid oxidation.

A comparative study of serum total thyroxine estimation on unextracted serum by radioimmunoassay and by competitive protein binding

A rapid and precise radioimmunoassay (RIA) for serum total thyroxine (T4) on as little as 1-10 mul of unextracted serum is described. Results in hypothyroidism (overt and borderline), in euthyroid subjects in pregnant and oestrogen-medicated subjects, and in hyperthyroidism (overt and borderline) are compared with the results on the same sera by an established competitive protein binding technique (Ames' Tetralute) on unextracted serum from a different laboratory. The correlation between the two methods was excellent (r= 0.94) and no significant difference between overall appeared to measure total T4 Reliaby in sera containing only 1-3 or 2-6 nmol/1. Both methods predicted the clinical outcome in borderline hypothyroidism and borderline hyperthyroidism equally well and both gave normal results in T3-toxicosis. It is concluded that both techniques reliably measure total T4- RIA appears to have advantages of sensitivity and precision (especially in the hypothroid range), of simplicity, and of low cost.

Serum triiodothyronine in solitary autonomous nodules of the thyroid

Seventeen patients with solitary autonomous nodules of the thyroid were studied. Eight had clinical features of hyperthyroidism though in some the clinical manifestations were mild. The serum T3 concentration was elevated in all patients with hyperthyroidism but the serum T4 and free thyroxine index were within the normal range in five. All patients with hyperthyroidism subsequently responded to treatment. These findings suggest a high incidence of preferential T3 hypersecretion in hyperthyoidism associated with solitary autonomous thyroid nodule. A further nine patients with single autonomous nodules were clinically euthyroid with normal serum T3 and T4 concentrations and remained euthyroid from 6 to 24 months on serial review.

Hormonal pattern of relapse in hyperthyroidism

22 patients with Grave's disease were followed up for up to a year after antithyroid drug therapy was discontinued. Clinical assessment and serum T3, T4, and thyroid-stimulating-hormone (T.S.H.) estimations were done serially and simultaneously. Serum T3 or T4 concentrations may be elevated briefly in the first few weeks after antithyroid drugs are stopped, as a rebound effect not necessarily indicative of subsequent relapsf. Clinical relapse of hyperthyroidism with subsequent improvement on antithyroid drugs occurred in 13 patients. Of these 13, serum T3 concentrations became elevated before serum T4 concentrations in 5, thus predicting the subsequent development of clinical hyperthyroidism. In the remaining 8 patients who relapsed, serum T4 was elevated a month before the serum T3. Hyperthyroidism was diagnosed clinically after elevated serum T3 concentrations in 11 patients and at the same time in 2 patients. The mean period of "biochemical hyperthyroidism" in these 11 patients was 12 weeks, with a range of 1 to 56 weeks. During this period 9 of the 11 had minor clinical changes attributable to hyperthyroidism. It is concluded that serial estimations of serum T3 provide the most reliable method of monitoring relapse in hyperthyroidism.

Ecologic studies of Venezuelan encephalitis virus in Peru during 1970-1971

Venezuelan encephalitis (VE) virus has intermittently produced epidemics and equine epizootics on the dry Pacific coastal plain of Peru since at least the 1930's. However, evidence that the virus exists in the Amazon region of Peru to the east of the Andes mountains was not obtained until antibodies were found in human sera collected in 1965, and 10 strains of the virus were isolated in a forest near the city of Iquitos, Peru during February and March 1971. Eight strains came from mosquitoes and two from dead sentinel hamsters. Three hamsters exposed in forests near Iquitos developed VE virus antibodies suggesting that hamster-benign strains also exist there. Antibody tests of equine sera revealed no evidence that VE virus was actively cycling during the late 1950's or 1960's in southern coastal Peru, where equine epizootics had occurred in the 1930's and 1940's. In northern coastal Peru bordering Ecuador, antibodies were present in equine sera, presumably residual from the 1969 outbreak caused by subtype I virus, since neutralizing antibody titers were higher to subtype I virus than to subtypes III or IV. No VE virus was detected in this northern region during the dry season of 1970 by use of sentinel hamsters. The possibility is considered that VE epidemics and equine epizootics on the Pacific coast of Peru are caused by movements of virus in infected vertebrates traversing Andean passes or in infected vertebrates or mosquitoes carried in airplanes from the Amazon region.