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Biomedical subjects

M Merle

Publications and source records attributed to M Merle.

At least 91 records · Page 5Linked to original sources
PubMed1986

Kinetic evidence for half-of-the-sites reactivity in tRNATrp aminoacylation by tryptophanyl-tRNA synthetase from beef pancreas.

The aminoacylation reaction catalyzed by the dimeric tryptophanyl-tRNA synthetase from beef pancreas was studied under pre-steady-state conditions by the quenched-flow method. The transfer of tryptophan to tRNATrp was monitored by using preformed enzyme-bis(tryptophanyl adenylate) complex. Combinations of either unlabeled or L-[14C]tryptophan-labeled tryptophanyl adenylate and of aminoacylation incubation mixtures containing either unlabeled tryptophan or L-[14C]tryptophan were used. We measured either the formation of a single labeled aminoacyl-tRNATrp per enzyme subunit or the turnover of labeled aminoacyl-tRNATrp synthesis. Four models were proposed to analyze the experimental data: (A) two independent and nonequivalent subunits; (B) a single active subunit (subunits presenting absolute "half-of-the-sites reactivity"); (C) alternate functioning of the subunits (flip-flop mechanism); (D) random functioning of the subunits with half-of-the-sites reactivity. The equations corresponding to the formation of labeled tryptophanyl-tRNATrp under each labeling condition were derived for each model. By use of least-squares criteria, the experimental curves were fitted with the four models, and it was possible to disregard models B and C as likely mechanisms. Complementary experiments, in which there was no significant excess of ATP-Mg over the enzyme-adenylate complex, emphasized an activator effect of free L-tryptophan on the rate of aminoacylation. This result disfavored model A. Model D was in agreement with all data. The analyses showed that the transfer step was not the major limiting reaction in the overall aminoacylation process.

Amino Acyl-tRNA Synthetases↗
PubMed1986

Tryptophanyl adenylate formation by tryptophanyl-tRNA synthetase from Escherichia coli.

By gel filtration and titration on DEAE-cellulose filters we show that Escherichia coli tryptophanyl-tRNA synthetase forms tryptophanyl adenylate as an initial reaction product when the enzyme is mixed with ATP-Mg and tryptophan. This reaction precedes the synthesis of the tryptophanyl-ATP ester known to be formed by this enzyme. The stoichiometry of tryptophanyl adenylate synthesis is 2 mol per mole of dimeric enzyme. When this reaction is studied either by the stopped-flow method, by the fluorescence changes of the enzyme, or by radioactive ATP depletion, three successive chemical processes are identified. The first two processes correspond to the synthesis of the two adenylates, at very different rates. The rate constants of tryptophanyl adenylate synthesis are respectively 146 +/- 17 s-1 and 3.3 +/- 0.9 s-1. The third process is the synthesis of tryptophanyl-ATP, the rate constant of which is 0.025 s-1. The Michaelis constants for ATP and for tryptophan in the activation reaction are respectively 179 +/- 35 microM and 23.9 +/- 7.9 microM, for the fast site, and 116 +/- 45 microM and 3.7 +/- 2.2 microM, for the slow site. No synergy between ATP and tryptophan can be evidenced. The data are interpreted as showing positive cooperativity between the subunits associated with conformational changes evidenced by fluorometric methods. The pyrophosphorolysis of tryptophanyl adenylate presents a Michaelian behavior for both sites, and the rate constant of the reverse reaction is 360 +/- 10 s-1 with a binding constant of 196 +/- 12 microM for inorganic pyrophosphate (PPi).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Monophosphate↗
PubMed1986

Joint reconstruction following trauma: comparison of microsurgical transfer and conventional methods: a report of 61 cases.

Joint reconstruction at the metacarpophalangeal or proximal interphalangeal levels remains a difficult problem in hand surgery. The authors reviewed sixty-one joints reconstructed acutely or electively allowing to compare Swanson spacer (30 joints), interpositional arthroplasty (4), non vascularized joint transfer (5) and vascularized joint transfer (21). Among these, two different techniques have been used: island compound transfer from a finger bank (10) and free vascularized transfer from the second toe (10) or from a non replantable finger (1). It is not worth while comparing different techniques applied to different indications. The only point which can be stressed is the better average range of movement of metacarpophalangeal reconstruction compared to that obtained at the proximal interphalangeal level.

Arthroplasty↗
PubMed1986

Sarcoid tenosynovitis in the hand. A case report and literature review.

We report a case of involvement of a finger flexor tendon by sarcoidosis. A review of twelve cases suggests that this is a rare manifestation of the illness that most often affects the finger extensors at the wrist. It tends to present in established sarcoidosis and is associated with a higher than usual incidence of polyarthritis. The main differential diagnosis would be tuberculous tenosynovitis. We suggest that a histological spectrum exists running from a predominantly cellular picture to one of fibrotic nodules, perhaps explaining previously described instances of pseudo-tumour. We would recommend tenosynovectomy in conjunction with corticosteroid therapy as the treatment of choice.

Female↗
PubMed1986

[Revascularization of digital avulsion injuries caused by rings].

The authors describe an original technique of ring fingers revascularization, avoiding two chief dangers met in the double vein grafts: the one of the joint and tendinous devascularization with its risks of stiffness, and the other one of the devascularization of the skin sheath with secondary necrosis or trophic trouble. The worse artery is resected and the defect is bridged by a long venous graft, the skin of the distal fingers being provided by the backflow.

Finger Injuries↗
PubMed1986

[Sympathectomy of the digital arteries in acro-syndromes].

Digital sympathectomy as proposed by Flatt and al. was performed on 12 Raynaud's diseases, 6 distal arteriopathy and 4 post-trauma ischemic syndrome. Operation was performed under tourniquet. The approach depends on the number of digits involved (Brünner at the proximal part of P1, transversal in the distal palmar crease, zigzag incision at the level of each intermetacarpal space). Under microscope, adventisectomy is started on a lateral side of the artery followed by the posterior side on at least 1 cm, using the adventitia avoid all direct manipulation of the vessels. Closing skin on an aspirative drainage and simple non compressive drainage is maintaining 4 days. Index pressure and arterial blood flow are measured. Results are bad for post-trauma ischemic syndrome and arteritis but encouraging in Raynaud's disease (7 patients asked for the same operation on the opposite side).

Adult↗
PubMed1985

Tryptophanamide formation by Escherichia coli tryptophanyl-tRNA synthetase.

When tryptophanyl-tRNA synthetase from Escherichia coli is allowed to react with L-tryptophan and ATP-Mg in the presence of inorganic pyrophosphatase, the fluorescence change of the reaction mixture reveals three or four sequential processes, depending on the buffer used. Quenched-flow and stopped-flow experiments show that the first two processes, which occur in the 0.001-1.0-s time scale, can be correlated to the formation of two moles of tryptophanyl-adenylate per mole of dimeric enzyme. These two processes are reversible by adding PPi, as seen in the fluorimeter. The third process leads to a reaction product that can no longer reform ATP after addition of PPi and that represents tryptophanyl-ATP ester, as demonstrated by thin-layer chromatography. This compound has been previously shown to be formed by tryptophanyl-tRNA synthetase from E. coli [K. H. Muench (1969) Biochemistry 8, 4872-4879]. Its formation is accompanied by a fluorescence decrease which reaches a minimum in about 30 min. The nature of the fourth process depends on the reaction conditions employed. In sodium bicarbonate or potassium phosphate buffer, the fourth process corresponds to the non-enzymatic hydrolysis of tryptophanyl-ATP ester. This spontaneous hydrolysis competes with formation of the ester and limits its concentration. Eventually, the progressive exhaustion of ATP brings the fluorescence intensity of the reaction mixture back to its initial value. In contrast, in ammonium bicarbonate buffer the previous third process is no longer visible, as evidenced by the absence of a fluorescence decrease beyond the fast initial quenching linked to the formation of tryptophanyl-adenylate. Instead, a fluorescence increase is observed. However, unlike the fourth process seen in sodium bicarbonate buffer, the fluorescence increase in ammonium bicarbonate is much larger than the initial fluorescence decrease linked to adenylate formation, the final fluorescence greatly surpassing the starting fluorescence signal. The reaction product of this process is tryptophanamide, as evidenced by high-performance liquid chromatography. Tryptophanamide formation is faster than that of tryptophanyl-ATP ester and is enzyme-catalyzed with a Km of 1 mM for ammonia and a rate constant of 5.7 min-1 at pH 8.3, 25 degrees C. The affinity of tryptophanamide for the protein is too weak to allow the formation of a significant concentration of enzyme-product complex. Tryptophanamide is therefore released in the reaction medium and its concentration reaches that of the limiting substrate.

Amino Acyl-tRNA Synthetases↗
PubMed1985

Immediate and prolonged effects of dihydroergocryptine after experimental vascular microsurgery.

An animal model of limb replantation has been utilized in order to evaluate the effects of dihydroergocryptine (DHEC, 0.1 mg/kg I.V.) on arterial and peripheral tissular blood flows after reperfusion. DHEC is a partial agonist of adrenergic receptors and is therefore liable to exert an action on arteriovenous shunts that remain abnormally opened after ischaemia. DHEC showed important efficacy in this model, increasing, in low doses, blood flow in sutured artery and peripheral tissue.

Animals↗
PubMed1985

Free vascularized nerve grafts: an experimental study in the rabbit.

An experimental animal model of a vascularized graft is presented as an alternative to recover faster function. The technique is described and the model compared to a conventional graft in the sciatic nerve of a rabbit. Results are evaluated with histological studies and quantified using a computer to measure the thickness of the myelin sheath as a correspondence factor of regeneration. Results showed a more favorable regeneration when a vascularized graft was used.

Animals↗
PubMed1985

Fractures of the hook of the hamate.

Fractures of the hook of the hamate are rare injuries. Six new cases are presented; the most usual mechanism is probably a direct blow to the area of the hook. The diagnosis, which can only be made by special roentgenographic techniques is usually missed at the acute phase. Most of the cases are diagnosed when painful non-union, fraying tendinitis of the flexor tendons to the ulnar fingers, ulnar or median nerve deficits appear. The adequate treatment is usually excision of the hook fragment.

Adult↗
PubMed1985

[Hueston's flap for reconstruction of loss of distal thumb substance].

The classical rotation flap described by J. Hueston involves the advancement of a denervated skin area on the distal stump. In distal amputations of the thumb, this flap should only be used on the lateral side in order to avoid creating a blind medial pulp. Furthermore, this leaves a proximal skin defect thereby exposing the neurovascular bundles. This secondary defect is best covered by a lateral triangular rotation flap.

Humans↗
PubMed1985

Homodigital neurovascular island flaps in hand surgery. A study of sixty cases.

The homodigital island flap is a useful technique in problem cases such as distal amputation of the pulp, atrophic or insensative pulp on the index finger or thumb and painful neuromas. In a series of 60 operations preformed by one surgeon with the SOS Main in Strasbourg, we describe the indications for, and results of, several different techniques: unipedical flaps either advanced or "exchanged" and bipedical flaps either advanced or retreated.

Adolescent↗