Biomedical subjects

J Cabanes

Publications and source records attributed to J Cabanes.

At least 19 recordsLinked to original sources

PubMed2004

Kinetic analysis of catechin oxidation by polyphenol oxidase at neutral pH.

Catechin oxidation by peach polyphenol oxidase was performed in a pH range of 3.5-8.0. At acidic pH, maximal spectral changes were observed at 390nm and at pH 7.5, at 430nm. Catechin oxidation was studied at pH 7.5 to avoid the formation of free radicals. The results obtained allowed us to propose a pathway for the enzymatic oxidation of catechin, according to which enzymatic oxidation produces the corresponding catechin-o-quinone, which suffers the nucleophilic attack of another catechin unit, leading to the formation of a dimer. This dimer is then oxidized by the enzymatically generated o-quinone. The progress curves obtained for catechin oxidation by PPO showed a lag period, whose length changed with enzyme and substrate concentrations, and which must have been caused by the chemical reactions taking place after the enzymatic reaction. The results obtained by simulation of the model produced the same qualitative dependences as obtained experimentally.

Animals↗

PubMed2003

A continuous spectrophotometric assay for phospholipase A(2) activity.

This paper describes a simple continuous spectrophotometric method for assaying phospholipase A(2) (PLA(2)) activity. The procedure is based on a coupled enzymatic assay, using dilinoleoyl phosphatidylcholine as phospholipase substrate and lipoxygenase as coupling enzyme. The linoleic acid released by phospholipase was oxidized by lipoxygenase and then phospholipase activity was followed spectrophotometrically by measuring the increase in absorbance at 234 nm due to the formation of the corresponding hydroperoxide from the linoleic acid. The optimal assay concentrations of hog pancreatic phospholipase A(2) and lipoxygenase were established. PLA(2) activity varied with pH, reaching its optimal value at pH 8.5. Scans of the deoxycholate concentration pointed to an optimal detergent concentration of 3mM. Phospholipid hydrolysis followed classical Michaelis-Menten kinetics (V(m)=1.8 microM/min, K(m)=4.5 microM, V(m)/K(m)=0.4 min(-1)). This assay also allows PLA(2) inhibitors, such as p-bromophenacyl bromide or dehydroabietylamine acetate, to be studied. This method was proved to be specific since there was no activity in the absence of phospholipase A(2). It also has the advantages of a short analysis time and the use of commercially nonradiolabeled and inexpensive substrates, which are, furthermore, natural substrates of phospholipase A(2).

Deoxycholic Acid↗

PubMed2003

Determination of the phospholipase activity of patatin by a continuous spectrophotometric assay.

Patatin is a family of glycoproteins that accounts for 30-40% of the total soluble protein in potato (Solanum tuberosum L.) tubers. This protein has been reported to serve as a storage protein and also to exhibit lipid phospholipase activity. This paper describes a simple continuous spectrophotometric method for assaying patatin phospholipase activity. The procedure is based on a coupled enzymatic assay using [1,2-dilinoleoyl] PC as the phospholipase substrate and lipoxygenase as the coupling enzyme. In the procedure developed in this work, lipoxygenase oxidizes the linoleic acid released by the phospholipase activity of patatin. This activity can then be followed spectrophotometrically by recording the increase in absorbance at 234 nm that results from the formation of the corresponding hydroperoxide from linoleic acid by the action of lipoxygenase. The optimal assay concentrations of patatin and lipoxygenase were established. Phospholipase activity varied with pH, reaching its optimal value at pH 9.5. Scans of the deoxycholate concentration pointed to an optimal detergent concentration of 3 mM. Phospholipid hydrolysis followed classical Michaelis-Menten kinetics (Vm = 9.8 x 10(-3) micromol/min x microg protein, Km = 7.8 microM, Vm/Km = 1.3 min(-1) x microg protein). This method proved to be specific since there was no activity in the absence of patatin. It also had the advantages of a short analysis time and the use of commercially nonradiolabeled and inexpensive substrates, which are, furthermore, natural substrates of phospholipase.

Carboxylic Ester Hydrolases↗

PubMed2001

Hysteresis and positive cooperativity of iceberg lettuce polyphenol oxidase.

A kinetic study of the diphenolase activity of latent polyphenol oxidase (PPO), purified from Iceberg lettuce (Lactuca sativa L), revealed a sigmoid relationship between the reaction rate and the substrate concentration with a high Hill coefficient (n(H) = 3.8). This positive cooperativity had not been previously described for any PPO. Furthermore, the enzyme showed a lag phase in the expression of this activity, suggesting a hysteretic nature of the enzyme. The kinetic behavior, the latency and the lag phase varied at different steps of the purification process. PPO showed hyperbolic or cooperative kinetics depending on the pH assay and the sodium dodecyl sulfate (SDS) concentration. Substrate-induced slow conformational change of the oligomeric enzyme is suggested. The conformational change would be toward a more active enzyme form with higher affinity for the substrate and favoured by acid pH and SDS.

Catechol Oxidase↗

PubMed2001

An octaethylene glycol monododecyl ether-based mixed micellar assay for determining the lipid acyl hydrolase activity of patatin.

Patatin was extracted from potato tubers (Solanum tuberosum L. cv. Spunta) and purified to homogeneity by ammonium sulfate salt fractionation and one sole chromatographic step. A spectrophotometric mixed micellar assay for patatin lipid acyl hydrolase (LAH) activity was designed with the detergent octaethylene glycol monododecyl ether (C12E8). Patatin LAH used p-nitrophenyl butyrate (PNP-butyrate) as substrate when solubilized in (C12E8) micelles. In the mixed micellar system, patatin LAH responds to the PNP-butyrate surface concentration expressed as mol% (= [PNP-butyratel x 100/([detergentl critical micellar concentration)) and not to the molarity of PNP-butyrate. The kinetic parameters were determined; Vmax was independent of the mixed micelle concentration, as was Km, when expressed as mol%. However, Km was dependent on C12E8 concentration when expressed in molar concentration. C12E8/PNP-butyrate proved to be a reliable system for assaying patatin LAH activity and is superior to the commonly used Triton X-100 and SDS methods. It permits investigation of the substrate requirements of patatin LAH activity because the concentration-independent Km can be determined both in mol% and as the absolute number of substrate molecules per micelle. In addition, the detergent did not affect the enzyme activity.

Carboxylic Ester Hydrolases↗

PubMed2001

[Preoperative embolization in meningioma of the ponto-cerebellar angle. Indications and advantages].

Preoperative embolization of meningiomas has been performed in order to reduce surgical hemorrhage during the removal of these vascularized tumors. In this paper we emphasize the fact that occlusion of the tumoral vessels by artificial emboli produces an ischemic necrosis that greatly helps tumor exeresis. This is especially useful in meningiomas of certain localizations requiring complex surgical approaches. In our case, a giant ponto-cerebellar meningioma was dried up totally and then removed with relative ease through a conventional suboccipítal lateral craniectomy. The technique, indications and control of preoperative embolization are reviewed.

Adult↗

PubMed2001

Evidence for a tetrameric form of iceberg lettuce (Lactuca sativa L.) polyphenol oxidase: purification and characterization.

Polyphenol oxidase from iceberg lettuce (Lactuca sativa L.) chloroplasts was released from the thylakoid-membrane by sonication, and it was extensively purified to homogeneity as judged by SDS-PAGE. Purification was achieved by ammonium sulfate fractionation, gel-filtration chromatography, and ion-exchange chromatography. Two molecular forms were separated by gel-filtration chromatography with apparent molecular masses of 188 and 49 kDa. Both forms were characterized by sedimentation analysis with S(20,W) values of 10.2 and 4.1 S, respectively. For the high-molecular-weight form purified to homogeneity, denaturing SDS-PAGE indicated a molecular mass of 60 kDa. Thus, from these data we suggest that lettuce polyphenol oxidase is a tetramer of identical subunits.

Ammonium Sulfate↗

PubMed2001

Competitive inhibition of mushroom tyrosinase by 4-substituted benzaldehydes.

A kinetic study of the inhibition of mushroom tyrosinase by 4-substituted benzaldehydes showed that these compounds behave as classical competitive inhibitors, inhibiting the oxidation of L-3,4-dihydroxyphenylalanine (L-DOPA) by mushroom tyrosinase (o-diphenolase activity). The kinetic parameter (K(I)) characterizing this inhibition was evaluated for all of the seven compounds assayed. Cuminaldehyde showed the most potent inhibitory activity (K(I) = 9 microM). It also inhibited the oxidation of L-tyrosine by mushroom tyrosinase (o-monophenolase activity) in a competitive manner. The corresponding kinetic parameter for this inhibition was evaluated (K(I) = 0.12 mM).

Agaricales↗

PubMed1999

Characterization of monophenolase activity of polyphenol oxidase from iceberg lettuce.

Polyphenol oxidase (EC 1.14.18.1), a thylakoid membrane-bound enzyme, was isolated by sonication of osmotically shocked chloroplasts from iceberg lettuce (Lactuca sativa). The enzyme showed monophenolase activity when assayed on (p-hydroxyphenyl)propionic acid with 3-methyl-2-benzothiazolinone hydrazone in a reliable continuous spectrophotometric method, with high sensitivity, accuracy, and precision. The monophenolase activity showed a lag period before the steady-state rate (V(ss)) was reached. Both kinetic parameters, the lag period and the steady-state rate, depended on the pH, the enzyme and substrate concentrations, and the presence of catalytic amounts of o-diphenol. This activity shows inhibition by high substrate concentration. The experimental results correspond with the mechanism previously described for PPO from other sources. Kinetic constants K(m), V(max), and K(i) were determined.

Catechol Oxidase↗

PubMed1998

[Long-term results of surgical pharyngectomy (uvulo-palato-pharyngoplasty) versus office CO2 laser (L.A.U.P.) for the treatment of uncomplicated snoring].

Two treatments are habitually proposed for snoring without obstructive sleep apnea syndrome: the surgical pharyngotomy, and the treatment by laser done in the office. Our study analyses retrospectively, by telephone questionnaire, a group of 168 snorers, without obstructive sleep apnea syndrome, treated by pharyngotomy (n = 71) or CO2 laser (n = 97) between 1989 and 1993. Results after a mean follow-up of 5 years, with a minimal of 3 years, show for the two procedures the same efficacity, and an equivalent prevalence of side effects. The rate of satisfaction for the patient and her bed-partner is about 50%, in relation to a degradation of therapeutic effect in the long run. We propose to precisely the results and the indications of the surgery and the laser for treatment of uncomplicated rhonchopathy.

Adult↗

PubMed1997

Kinetic study of the suicide inactivation of latent polyphenoloxidase from iceberg lettuce (Lactuca sativa) induced by 4-tert-butylcatechol in the presence of SDS.

In plants, polyphenoloxidase undergoes an irreversible inactivation during the oxidation of o-diphenol to o-quinones. In the present paper, using latent polyphenoloxidase from iceberg lettuce (Lactuca sativa), in the presence of an activating agent, SDS, the kinetic parameters that characterize the enzyme during its action on the suicide substrate 4-tert-butylcatechol have been determined. The effect of pH has also been considered. It was seen that the presence of SDS in the reaction medium changed the kinetic parameters of the enzyme during suicide inactivation, this phenomenon depended on the SDS concentration up to saturating concentrations. Variations were also observed in the kinetic parameters at pH values below 5 where SDS provoked inactivation of the enzyme. This differing kinetic behaviour during suicide inactivation in the presence of SDS may be caused by the conformational changes provoked by SDS in the enzyme in latent state. Thus, polyphenoloxidases showing suicide inactivation would present an enzymatic activity resulting from the balance between the activation process and suicide inactivation.

Antioxidants↗

PubMed1997

Delayed extradural hematoma after mild head injury: report of three cases.

BACKGROUND: Extradural hematoma has been classically considered to be an acute complication of head injury whose maximum development takes place in the minutes following trauma. Delayed extradural hematoma (DEH) is defined on the basis of an exclusively radiologic criterion: epidural hematoma that is not present in the first neuroradiologic examination made after trauma but that appears in sequential neuroradiologic examinations during patient evolution. This is an infrequent complication that usually appears in hypotensive multiple trauma patients or is related to severe head injury with other intracranial lesions. CASE DESCRIPTION: We present three cases of DEH after mild head injury (GCS > 12) without associated intracranial or traumatic systemic lesions. Therefore, those usually considered to be "protective mechanisms" responsible for delayed development of an extradural hematoma were absent in our three patients. Diagnosis was attained by means of repetition of cranial computed tomography (CT) scan after neurologic impairment was noted. Surgical evacuation of DEH was immediately performed after diagnosis. Postoperative outcome was favorable in two patients who suffered DEH in the supratentorial compartment. One patient who presented a posterior fossa DEH died 3 days after surgery. CONCLUSIONS: Early diagnosis and immediate treatment have proved to be essential for improving the prognosis of patients affected by DEH. Hospital admission under neurologic observation is recommended for patients who have sustained mild head injury associated with those factors that are related to the development of DEH, including GCS score under 15 or the detection of a skull fracture. Normality of a CT scan does not rule out subsequent appearance of delayed traumatic lesions.

Adolescent↗

PubMed1996

[Frontal mucoceles of orbital or cerebral extension: therapeutic strategy].

The aim of this study was to investigate ten patients who underwent surgery for mucoceles of the frontal sinus. Bicoronal direct access was required by the localization of the mucocele limited to the frontal sinuses, its extension to the orbit and/or the brain and because of the anatomy of the frontal sinuses (large size, lateral horn...) as evidenced at imaging. Direct access to the frontal sinuses was achieved in 9 patients allowing marsupialization associated with repermeabilization of the naso-frontal duct (7 cases) or exeresis of the mucocele by cranialization (2 cases). Mean follow-up is 27 months. Repermeabilization of the naso-frontal duct was effective in 7 out of 8 cases. There were no complications after cranialization and no recurrence has been observed. Drainage of frontal mucoceles is a first intention strategy. In case of complication or recurrence, cranialization of the frontal sinuses would appear to be better than an exclusion-filling procedure.

Adult↗

PubMed1995

[Laser CO2 arytenoidectomy by endoscopic approach in bilateral laryngeal paralysis. Apropos of 45 cases].

Between 1980 and 1993, 45 patients with bilateral cord abductor paralysis were treated by carbon dioxide endoscopic laser arytenoidectomy. Thyroid surgery was the main cause of bilateral laryngeal palsy (67%). Seven patients, who were tracheotomised before treatment, were decanulated. Ninety-one percent of the patients recovered physiologic respiration. The follow up period lasted from one month to thirteen one-half years. Advantages and disadvantages of laser arytenoidectomy are compared with other techniques.

Adult↗

PubMed1995

[Endonasal treatment of iatrogenic or spontaneous cerebrospinal rhinorrhea of the anterior cranial fossa].

There is a 25% risk of meningitis in case of cerebrospinal fluid rhinorrhea from the anterior cranial fossa. Treatment usually is based on neurosurgery when medical management is unsuccessful. The risk of morbidity and mortality in such operations is important and recurrence is observed in 25% of the cases. The development of endonasal surgery has increased the incidence of iatrogenic breaches but has also allowed the development of new techniques for closing breaches. Certain authors recently published a recent series of patients treated via the endonasal route. We present here six cases of cerebrospinal fluid rhinorrhoea from the anterior cranial fossa treated at the Foch Hospital. Etiology was iatrogenic in 4 cases, trauma in 1 and spontaneous in 1. The operative technique and mid-term results are presented. Cure was achieved in all cases after a mean follow-up of 2 years. One patient with osteopetrosis of the cranial floor who underwent neurosurgical decompression of the optic nerve complained of recurrent rhinorrhoea which could not be confirmed by endoscopy nor by imaging. Early endoscopic treatment of cerebrospinal fluid rhinorrhoea should be the first intention option as it preserves olfactive function, limits operative morbidity and mortality and leaves open the option of neurosurgery in case of failure.

Adult↗

PubMed1995

[Treatment of velopharyngeal stenosis after pharyngotomy for chronic snoring. Apropos of 13 cases].

Velopharyngeal stenosis is a rare complication of pharyngotomy (UPPP) for chronic snoring. Its treatment is hard because of its recidivant feature. The aim of this study was to determine a therapeutic strategy accorded to each stenosis from clinical and anatomical features of 13 velopharyngeal stenosis. Therapeutic behavior was function of patients complains, of the ground (associated chronic rhinosinusitis and obstructive sleep apnea) and clinical findings (partial or total stenosis, tonsil remainders, short or long residual soft palate). From these data, treatment was medical (1 case) or surgical (12 cases), searching lateral velopharyngeal mucosa recovery in order to avoid recidive of stenosis. This aim needed locoregional mucosal grafts in 4 patients with short soft palate. Patients complains were improved in all cases and there was no patient with recurrence of stenosis. The best treatment of velopharyngeal stenosis still remains a preventive one, by respecting a severe surgical technique during pharyngotomy for chronic snoring.

Adult↗

PubMed1994

Kojic acid, a cosmetic skin whitening agent, is a slow-binding inhibitor of catecholase activity of tyrosinase.

It was found that kojic acid, which is used in cosmetics for its excellent whitening effect, inhibits catecholase activity of tyrosinase in a non-classical manner. A decrease in the initial velocity to a steady-state inhibited velocity can be observed over a few minutes. This time-dependence, which is unaltered by prior incubation of the enzyme with the inhibitor, is consistent with a first-order transition. The kinetic data obtained correspond to those for a postulated mechanism that involves the rapid formation of an enzyme inhibitor complex that subsequently undergoes a relatively slow reversible reaction. Kinetic parameters characterizing this type of inhibition were evaluated by means of nonlinear regression of product accumulation curves.

Animals↗

PubMed1988

Chemical and enzymic oxidation by tyrosinase of 3,4-dihydroxymandelate.

Tyrosinase usually catalyses the conversion of monophenols into o-diphenols and the oxidation of diphenols to the corresponding o-quinones. Sugumaran [(1986) Biochemistry 25, 4489-4492] has previously proposed an unusual oxidative decarboxylation of 3,4-dihydroxymandelate catalysed by tyrosinase. Our determination of the intermediates involved in the reaction demonstrated that 3,4-dihydroxybenzaldehyde is not the first intermediate appearing in the medium during the enzymic reaction. Re-examination of this new activity of tyrosinase has demonstrated that the product of the enzyme action is the o-quinone, which, owing to its instability, evolves to the final product, 3,4-dihydroxybenzaldehyde, by a chemical reaction of oxidative decarboxylation.

Ascorbic Acid↗