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Biomedical subjects

C Michaud

Publications and source records attributed to C Michaud.

At least 19 recordsLinked to original sources
PubMed1992

Inhibition of the chymotrypsin-like activity of the pituitary multicatalytic proteinase complex.

The multicatalytic proteinase complex (MPC), also referred to as proteasome, is a large molecular mass intracellular particle (approximately 700 kDa), which exhibits three distinct proteolytic activities designated as chymotrypsin-like, trypsin-like, and peptidylglutamyl-peptide hydrolyzing (PGPH), all sensitive to inhibition by 3,4-dichloroisocoumarin (DCI). The presence of a component resistant to inhibition by DCI with an apparent preference toward bonds on the carboxyl side of branched-chain amino acids has also been recently established. Peptide aldehydes and peptide alpha-keto esters containing a hydrophobic residue in the P1 position have been tested as potential inhibitors of the chymotrypsin-like activity. Three peptide aldehydes (benzyloxycarbonyl)-Leu-Leu-phenylalaninal (Z-LLF-CHO), N-acetyl-Leu-Leu-norleucinal (Ac-LLnL-CHO), and N-acetyl-Leu-Leu-methioninal (Ac-LLM-CHO) were found to be slow-binding reversible inhibitors with Ki values of 0.46, 5.7, and 33 microM, respectively. The simplest kinetic model for inhibition is consistent with a mechanism involving a slow and reversible association of the enzyme with the inhibitor to form a EI complex. The aldehyde inhibitors also inhibited the trypsin-like and PGPH activities of the complex albeit with much higher Ki values than those for chymotrypsin-like activity. Z-LLF-CHO, the most selective of the three aldehydes, did not inhibit the PGPH activity at concentrations of up to 200 microM and inhibited the trypsin-like activity with a Ki approximately 2 orders of magnitude higher than that for the chymotrypsin-like activity. The activity of the DCI-resistant component was not affected by Z-LLF-CHO.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

A 3,4-dichloroisocoumarin-resistant component of the multicatalytic proteinase complex.

The multicatalytic proteinase complex (MPC) exhibits three proteolytic activities designated as trypsin-like, chymotrypsin-like, and peptidylglutamyl-peptide hydrolyzing (PGPHA). Evidence based on inhibitor and specificity studies indicates that each of the three activities is associated with a different component of the complex. Inactivation of the three activities by the serine proteinase inhibitor, 3,4-dichloroisocoumarin (DCI), reveals the presence of an additional DCI-resistant component that cleaves natural peptides including neurotensin, dynorphin, angiotensin II, the oxidized B-chain of insulin, and also proinsulin at a rate greater than that of the native uninhibited complex. Examination of the reaction products of neurotensin (NT) and proinsulin degradation showed cleavage of the Ile12-Leu13 bond in NT and cleavage of the Leu44-Ala45 and Val39-Gly40 bonds within the connecting peptide (C-chain) of bovine proinsulin, suggesting preferential cleavage of bonds on the carboxyl side of branched chain amino acids. Although resistant to inhibition by DCI, the component was sensitive to inhibition by the isocoumarin derivatives, 7-amino-4-chloro-3-[3-(isothioureido)propoxy]isocoumarin and 4-chloro-7-guanidino-3-(2-phenylethoxy)isocoumarin. Degradation of NT was activated by leupeptin, chymostatin, and antipain indicating that binding of these aldehyde inhibitors at one site can stimulate proteolytic activity at a different site of the complex. The DCI-resistant component seems to constitute a major component of the complex active in degradation of natural peptides and proteins.

Amino Acid Sequence↗
PubMed1992

[Heart valve surgery and associated diseases in aged subjects].

The object of this study was to assess the additional risk related to associated pathology in patients aged 70 or over undergoing valvular heart surgery. Two hundred and thirty nine patients aged 70 to 87 years (average 74.6 +/- 3.2) underwent this form of surgery between October 1979 and June 1989. Sixty seven had coronary artery disease, 26 had atherosclerotic occlusive peripheral arterial disease, and 149 had one or more extracardiovascular pathology. Two hundred and thirteen patients underwent monovalvular and 26 bivalvular replacement. Coronary bypass was associated in 25 cases. Eighteen patients (7.5%) died in the 30 days following surgery. The perioperative mortality was not significantly greater in patients with extra-cardiac pathology (9.4% vs 4.4%; NS), in patients with coronary artery disease (11.9% vs 5.8%; NS), in patients with respiratory failure and FEV1 < 1 litre (1 death out of 20 cases) or in patients with renal failure and serum creatinine levels > or = 175 mumol/l (20% vs 6.3%, NS). Respiratory failure was the only extra-cardiac variable identified with increased perioperative morbidity. The perioperative mortality of elderly patients with valvular heart disease is greater than that of patients under 70 years of age (6.4% vs 2.1%) in our experience of the last 6 years p < 0.01). Associated arterial and extra-cardiac pathology does not significantly increase the mortality and strict selection of elderly inoperable patients together with improved surgical techniques and postoperative care has considerably reduced perioperative morbidity and mortality in this group of patients.

Aged↗
PubMed1991

Regulation of the peptidylglutamyl-peptide hydrolyzing activity of the pituitary multicatalytic proteinase complex.

The finding that the activity of the multicatalytic proteinase complex (MPC) is greatly activated by low concentrations of sodium dodecyl sulfate (SDS) and fatty acids led to the proposal that the proteolytic activity of the complex is latent and that activation is needed for expression of full activity. Kinetic examination of the nature of the latency with Cbz-Leu-Leu-Glu-2-naphthylamide, a substrate cleaved by the peptidylglutamyl-peptide hydrolyzing activity (PGPH activity) of the complex, showed that plots of velocity versus substrate concentration yield sigmoidal curves, implying the presence of two or more substrate binding sites and the presence of cooperative interactions between the sites. Hill plots of log [v/(Vmax-v)] versus log [S] gave slopes with a Hill coefficient of 2.2-2.4, suggesting that more than two subunits are expressing the PGPH activity. At saturating substrate concentrations, SDS and lauric acid exposed a masked component of PGPH activity that was about equal in magnitude to the overt activity measured in the absence of these detergents, showing that under the latter conditions only about half of the enzyme activity is expressed. Activation by SDS and lauric acid was greater at low than at high substrate concentrations and was associated with a shift of the substrate concentration at half-Vmax (apparent Km) toward lower values. The decrease in the apparent Km in the presence of SDS (but not in the presence of lauric acid) was associated with a decrease in cooperativity. The presence of at least two distinct PGPH activity components with different reactivities was also indicated by the finding of two distinct inactivation rate constants in reactions with 3,4-dichloroisocoumarin, an irreversible inhibitor of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effects of breakfast-size on short-term memory, concentration, mood and blood glucose.

Effects of breakfast size on blood glucose, mood, short-term memory and concentration were assessed in 319 adolescents (age 13-20 years) in real-life setting. Mean energy increase of 63% over habitual breakfast had no effect on blood glucose or late morning mood. High energy intake from breakfast had a beneficial effect on immediate recall in short-term memory evaluated on the whole sample. However, concentration appeared to be impaired by a high caloric breakfast. There were no differences in the studied parameters according to energy supplement size. The present results are consistent with suggestions that meal size supplement has an effect on cognitive function.

Adolescent↗
PubMed1990

Over-production, purification and properties of the uridine-diphosphate-N-acetylmuramoyl-L-alanyl-D-glutamate: meso-2,6-diaminopimelate ligase from Escherichia coli.

The UDP-N-acetylmuramoyl-L-alanyl-D-glutamate:meso-2,6-diaminopimelate ligase was over-produced and purified from two plasmid-harbouring strains of Escherichia coli. The first strain, E. coli JM83(pHE5), gave a 15-fold over-production relative to parental strain. The enzyme could be partially purified (8.8-fold) by ion-exchange chromatography. With the second strain, E. coli JM83(pMLD25), a very strong over-production was obtained, since the enzyme represented about 20% of the cytoplasmic proteins. Purification yielded 77% protein homogeneity. However, the enzymatic activity, which was very unstable, was lost during the purification procedure. Several properties of the enzyme were studied. The enzyme gave maximal activity around pH 8. The isoelectric point was 5.2. The activity was increased by potassium phosphate. Reverse and exchange reactions could be catalysed. The N-terminal sequence of the protein was determined and correlated with the nucleotide sequence of the murE gene. The actual initiation codon was assigned.

Amino Acid Sequence↗
PubMed1990

A study of financial resources devoted to research on health problems of developing countries.

The Commission on Health Research for Development is an independent, international commission composed of 12 leaders from the fields of health research, social science research and development policy. Chaired by John Evans, the other Commissioners are Gelia Castillo, vice-chair, F. H. Abed, Sune Bergstrom, Doris Calloway, Esmat Ezzat, Demissie Habte, Walter Kamba, Adetokumbo Lucas, Adolfo Martinez-Palomo, Saburo Okita and V. Ramalingaswami. The Commission began its work in November 1987, charged with analysing the strengths, weaknesses and gaps in current research on health problems of developing countries, and making proposals and promoting action for improvement. The Commission is sponsored by a variety of foundations, bilateral donor agencies, and international organizations. The Commission's report was published in the spring of 1990. As part of the work of the Commission Secretariat, we have undertaken a study of financial resources devoted to research on the health problems of developing countries. The study which began in May 1988 has three objectives: (i) To describe the current pattern of funding for research on the health problems of developing countries. (ii) To provide a baseline against which future trends and/or new programmes can be measured. (iii) To explore the possibility of an ongoing information system on research on health problems of developing countries.

Developing Countries↗
PubMed1989

Pituitary multicatalytic proteinase complex. Specificity of components and aspects of proteolytic activity.

The 700-kDa multicatalytic proteinase complex from bovine pituitaries separates in polyacrylamide gel electrophoresis under dissociating and reducing conditions into 11 components with molecular masses ranging from 21 to 32 kDa. No higher molecular mass components were detected. A rabbit polyclonal antibody raised against the complex recognizes five immunoreactive components. As reported previously, the complex exhibits three distinct proteolytic activities designated as chymotrypsin-like, trypsin-like, and peptidylglutamyl-peptide hydrolyzing activities. All three activities are rather rapidly inactivated by 3,4-dichloroisocoumarin, a general serine protease inhibitor, however, the pseudo-first-order rate constants of inactivation of the three components differ within a wide range, with the chymotrypsin-like activity being most sensitive to inhibition. The peptidylglutamyl-peptide hydrolyzing activity is greatly activated by low concentrations of sodium dodecyl sulfate and fatty acids and seems to constitute the main component responsible for degradation of protein substrates. In addition to cleaving bonds on the carboxyl side of glutamyl residues, this activity also cleaves, albeit at a slower rate, bonds on the carboxyl side of hydrophobic residues; however, the secondary specificity of this component is clearly different from the chymotrypsin-like activity. Heparin selectively activates the chymotrypsin-like activity. The complex cleaves rapidly both native and dephosphorylated beta-casein in a reaction greatly accelerated by low concentrations of sodium dodecyl sulfate. The nature of proteolytic products, and also the rate of formation of acid-soluble, ninhydrin-reactive products, is different for the phosphorylated and dephosphorylated form of beta-casein, indicating that the degree of phosphorylation influences the rate and pattern of proteolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1989

[Nutrition behavior in adolescent students (15-19 years of age) in the Nancy metropolitan area. A comparison with the recommended nutritional intake of the French population].

This paper describes the food behavior of 495 adolescents (15-19 years old) sample living in Nancy (France). The results are compared with the Recommended Dietary Allowances (RDA) for French adolescent population. The RDA are not satisfied for important percentages of girls for the daily energy intake (26.3% of girls have allowances less than 30% RDA), for the calcium intake (28.7% of girls have allowances less than 40% RDA), and for the protein intake (17.6% of girls have allowances less than 20% RDA). Lipids consumption is excessive (19.9% of boys and 23.4% of girls have allowances greater than 20% RDA) and energy intake from breakfast are low (25% of adolescents provide less 10% of daily energy intake by breakfast) for all these teen-agers. These results confirm the data observed in two others studies concerning the food behavior of French adolescents.

Adolescent↗
PubMed1988

Substrate-related potent inhibitors of brain metalloendopeptidase.

Rat brain metalloendopeptidase (EC 3.4.24.15) generates Leu- and Met-enkephalin from several larger opioid peptides and is capable of degrading a number of neuropeptides. Substrate-related N-(1-carboxy-3-phenylpropyl) peptide derivatives were synthesized and tested for enzyme inhibition. The best of these derivatives, N-[1(RS)-carboxy-3-phenylpropyl]-Ala-Ala-Tyr-p-aminobenzoate, inhibited the enzyme in a competitive manner with a Ki of 16 nM. The data indicate that the carboxyl group of the N-(1-carboxy-3-phenylpropyl) moiety coordinates with the active site zinc atom and that the remaining part of the inhibitor is necessary for interaction with the substrate recognition site of the enzyme. Replacement of the 1-carboxy-3-phenylpropyl group by a carboxymethyl group decreased the inhibitory potency by more than 3 orders of magnitude, emphasizing the importance of the hydrophobic phenyl group for inhibitor binding to a hydrophobic pocket at the S1 subsite. Replacement of the Tyr residue by an Ala residue decreased the inhibitory potency by more than 20-fold. Changes in the structure of the residue interacting with the S1' subsite could cause a more than 60-fold change in inhibition. The inhibitors were either ineffective or only weakly inhibitory against membrane-bound metalloendopeptidase ("enkephalinase", EC 3.4.24.11), an enzyme highly active in rabbit kidney but also present in brain. The data indicate the presence of an extended binding site in the enzyme with residues interacting with S1, S1', and S3' subsites largely determining inhibitor binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Endopeptidase-24.15 is the primary enzyme that degrades luteinizing hormone releasing hormone both in vitro and in vivo.

The concentration of luteinizing hormone releasing hormone (LHRH) (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2), which reaches the anterior pituitary via the hypothalamo-hypophyseal portal system, appears to be controlled in part by the rate of LHRH degradation within the hypothalamus and/or pituitary. Specific, active site-directed endopeptidase inhibitors synthesized in our laboratory were used to identify the enzyme(s) involved in LHRH degradation by hypothalamic and pituitary membrane preparations, and by an intact anterior pituitary tumor cell line (AtT20). Incubation of LHRH with pituitary and hypothalamic membrane preparations led to the formation of pGlu-His-Trp (LHRH1-3) as the main reaction product. Under the same conditions, addition to the incubation mixtures of captopril, an inhibitor of the angiotensin converting enzyme, led to accumulation of pGlu-His-Trp-Ser-Tyr (LHRH1-5) and, to a lesser extent, pGlu-His-Trp-Ser-Tyr (LHRH1-6). The degradation of LHRH and the formation of the N-terminal tri- and pentapeptides was blocked by N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate (cFP-AAF-pAB), a specific, active site directed inhibitor of endopeptidase-24.15. Some inhibition of LHRH degradation and formation of the N-terminal hexapeptide was also obtained in the presence of N-[1-carboxy-2-phenylethyl]-Phe-p-aminobenzoate (cFE-F-pAB), an inhibitor of endopeptidase-24.11. Similar results were obtained with AtT20 cell membranes and with intact AtT20 cells in monolayer culture. Following cleavage by endopeptidases the C-terminal part of LHRH was rapidly degraded by aminopeptidases. Superactive analogs of LHRH in which Gly6 was replaced by a D-amino acid are resistant to degradation by both endopeptidase-24.11 and -24.15. In vivo, when LHRH was injected directly into the third ventricle of rats, the presence of cFP-AAF-pAB inhibited LHRH degradation. It is concluded that LHRH degradation is primarily initiated by the membrane-bound form of endopeptidase-24.15 to yield pGlu-His-Trp-Ser-Tyr and to a lesser extent by endopeptidase-24.11 to yield pGlu-His-Trp-Ser-Tyr-Gly.

Animals↗
PubMed1988

Incorporation of LL-diaminopimelic acid into peptidoglycan of Escherichia coli mutants lacking diaminopimelate epimerase encoded by dapF.

Recently a dapF mutant of Escherichia coli lacking the diaminopimelate epimerase was found to have an unusual large LL-diaminopimelic acid (LL-DAP) pool as compared with that of meso-DAP (C. Richaud, W. Higgins, D. Mengin-Lecreulx, and P. Stragier, J. Bacteriol. 169:1454-1459, 1987). In this report, the consequences of high cellular LL-DAP/meso-DAP ratios on the structure and metabolism of peptidoglycan were investigated. For this purpose new efficient high-pressure liquid chromatography techniques for the separation of the DAP isomers were developed. Sacculi from dapF mutants contained a high proportion of LL-DAP that varied greatly with growth conditions. The same was observed with the two DAP-containing precursors, UDP-N-acetylmuramyl-tripeptide and UDP-N-acetylmuramyl-pentapeptide. The limiting steps for the incorporation of LL-DAP into peptidoglycan were found to be its addition to UDP-N-acetylmuramyl-L-alanyl-D-glutamate and the formation of the D-alanyl-DAP cross-bridges. The Km value of the DAP-adding enzyme for LL-DAP was 3.6 x 10(-2) M as compared with 1.1 x 10(-5) M for meso-DAP. When isolated sacculi were treated with Chalaropsis N-acetylmuramidase and the resulting soluble products were analyzed by high-pressure liquid chromatography, the proportion of the main peptidoglycan dimer was lower in the dapF mutant than in the parental strain. Moreover, the proportion of LL-DAP was higher in the main monomer than in the main dimer, where it was almost exclusively located in the donor unit. There are thus very few D-alanyl-LL-DAP cross-bridges, if any. We also observed that large amounts of LL-DAP and N-succinyl-LL-DAP were excreted in the growth medium by the dapF mutant.

Amino Acid Isomerases↗
PubMed1987

Partial purification and specificity studies of the D-glutamate-adding and D-alanyl-D-alanine-adding enzymes from Escherichia coli K12.

The D-glutamate-adding and D-alanyl-D-alanine-adding enzymes from Escherichia coli were partially purified by fast protein liquid chromatography on an anion exchanger. Their relative molecular masses, determined by gel filtration on Superose 12, were 54,000 +/- 2000 and 51,000 +/- 2000, respectively. In order to investigate the specificity of these ligases, several compounds derived from their respective nucleotide substrates were prepared. In the case of the D-Glu-adding enzyme, DDP-MurNAc-L-Ala (DDP = dihydrouridine 5'-diphosphate) and P1-MurNAc-L-Ala were substrates of the reaction. In the case of the D-Ala-D-Ala-adding enzyme, only DDP-MurNAc-L-Ala-D-Glu(-meso-A2pm) was a substrate; P1-MurNAc-L-Ala-D-Glu(-meso-A2pm) was neither a substrate nor an inhibitor. Concerning the amino acid site of the D-Glu-adding enzyme, even closely related analogues of D-glutamate hardly inhibited the reaction.

Chromatography↗
PubMed1986

Substrate and inhibitor studies of thermolysin-like neutral metalloendopeptidase from kidney membrane fractions. Comparison with bacterial thermolysin.

The inhibitory constants of a series of synthetic N-carboxymethyl peptide inhibitors and the kinetic parameters (Km, kcat, and kcat/Km) of a series of model synthetic substrates were determined for the membrane-bound kidney metalloendopeptidase isolated from rabbit kidney and compared with those of bacterial thermolysin. The two enzymes show striking similarities with respect to structural requirements for substrate binding to the hydrophobic pocket at the S1' subsite of the active site. Both enzymes showed the highest reaction rates with substrates having leucine residues in this position while phenylalanine residues gave the lowest Km. The two enzymes were also inhibited by the same N-carboxymethyl peptide inhibitors. Although the mammalian enzyme was more susceptible to inhibition than its bacterial counterpart, structural variations in the inhibitor molecules affected the inhibitory constants for both enzymes in a similar manner. The two enzymes differed significantly, however, with respect to the effect of structural changes in the P1 and P2' positions of the substrate on the kinetic parameters of the reaction. The mammalian enzyme showed the highest reaction rates and specificity constants with substrates having the sequence -Phe-Gly-Phe- or -Phe-Ala-Phe- in positions P2, P1, and P1', respectively, while the sequence -Ala-Phe-Phe- was the most favored by the bacterial enzyme. The sequence -Gly-Gly-Phe- as found in enkephalins was not favored by either of the enzymes. Of the substrates having an aminobenzoate group in the P2' position, the mammalian enzyme favored those with the carboxyl group in the meta position while the bacterial enzyme favored those with the carboxyl group in the para position.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1985

Specificity of the uridine-diphosphate-N-acetylmuramyl-L-alanyl-D-glutamate: meso-2,6-diaminopimelate synthetase from Escherichia coli.

To investigate the specificity of the uridine-diphosphate-N-acetylmuramyl-L-alanyl-D-glutamate: meso-2,6-diaminopimelate synthetase, various compounds mimicking more or less different parts of the UDP-MurNAc-L-Ala-D-Glu substrate were prepared. Their size ranged from that of uridine or L-Ala-D-Glu to that of the whole nucleotide substrate. Chemical synthesis led to N alpha-acyl-dipeptides, in which the acyl group mimicked the MurNAc moiety, and to glycopeptides MurNAc(alpha or beta-Me)-L-Ala-D-Glu, in which the anomeric function is blocked. Partial degradation or chemical modification of the substrate UDP-MurNAc-L-Ala-D-Glu afforded: MurOHNAc-L-Ala-D-Glu, P1-MurNAc-L-Ala-D-Glu, and DDP-MurNAc-L-Ala-D-Glu (DDP = dihydrouridine-diphosphate). All these compounds were tested as substrates or (and) inhibitors of the reaction catalyzed by the A2pm-adding enzyme, which, after partial purification, was obtained in two active forms. Among the compounds tested as substrates, only DDP-MurNAc-L-Ala-D-Glu was a good one. The Km for this compound was 97 microM versus 55 microM for the natural substrate. Among the various compounds tested as inhibitors, only P1-MurNAc-L-Ala-D-Glu and MurNAc(alpha or beta-Me)-L-Ala-D-Glu had a significant inhibitory effect at 1mM. Apparently, no particular portion of the molecule is predominantly responsible for its recognition by the enzyme. In other words, multiple sites located over the whole molecule are required for a proper recognition and determine the high specificity of this activity. Therefore, to obtain efficient competitive inhibitors it is necessary to synthesize molecules very similar in size and structure to the natural substrate.

Binding Sites↗