Search PubMed⌕ Search

Biomedical subjects

G Murphy

Publications and source records attributed to G Murphy.

At least 253 records · Page 14Linked to original sources
PubMed1994

Volume of distribution and fractional clearance of urea in amputees on continuous ambulatory peritoneal dialysis.

OBJECTIVES: To demonstrate the effects of amputation on the estimates of urea volume of distribution (V) and KT/V urea in continuous ambulatory peritoneal dialysis (CAPD) patients and to present a method for correcting the errors created by the uncorrected anthropometric formulas estimating V. DESIGN: (1) A mathematical analysis of the error and the correction proposed was performed. (2) Urea kinetic modeling with uncorrected and corrected estimates utilizing both the Watson and the Hume anthropometric formulas was performed in amputees on CAPD. SETTING: Subjects were recruited from four dialysis units in one city: one Veterans Affairs unit, one university-affiliated unit, and two community units. PATIENTS: Fourteen amputees on CAPD:12 with unilateral leg amputation and 2 with bilateral leg amputation, at the same length of the leg, were studied. INTERVENTIONS: Urea kinetic studies were performed in 24-hour drained dialysate and urine specimens. MAIN OUTCOME MEASURES: Uncorrected and corrected estimates of V and KT/V urea were compared to each other and to the predictions of the mathematical model. Body weights corresponding to uncorrected and corrected V estimates were compared to the actual body weights. RESULTS: (1) The mathematical model predicts that uncorrected estimates by the anthropometric formulas will falsely characterize unilateral amputees as leaner than they are and bilateral amputees as more obese than they are. (2) In unilateral amputees studied with the Watson formulas, uncorrected V was 0.546 +/- 0.023 L/kg and corrected V was 0.520 +/- 0.023 L/kg (p < 0.001). Corresponding weekly KT/V urea values were 1.97 +/- 0.14 and 2.07 +/- 0.14, respectively (p < 0.001). Similar results were obtained with the Hume formulas. In bilateral leg amputees studied with the Watson formulas, uncorrected V was 0.479 +/- 0.022 L/kg and corrected V was 0.514 +/- 0.023 L/kg. Corresponding KT/V estimates were 2.11 +/- 0.45 and 1.96 +/- 0.14, respectively. The differences were even greater with the Hume formulas. Estimates of body weight calculated from corrected V values were equal to actual weight measurements, whereas those calculated from uncorrected V values were lower than actual body weight measurements in unilateral amputees, and much higher than actual body weight measurements in bilateral amputees. CONCLUSION: Uncorrected anthropometric estimates falsely characterize unilateral amputees as leaner than they actually are and bilateral amputees, amputated at the same leg length, as more obese than they actually are. Uncorrected KT/V estimates are, therefore, falsely low in unilateral amputees, and falsely high in bilateral amputees. The proposed correction of the anthropometric formulas provides estimates agreeing closely with dietary estimates of body composition. Further studies are needed to define the accuracy of the corrected formulas.

Aged↗
PubMed1993

Sites of nidogen cleavage by proteases involved in tissue homeostasis and remodelling.

The cleavage of recombinant mouse nidogen in its native form was examined with granule-stored proteases (leucocyte elastase, mast-cell chymase), blood proteases (thrombin, plasmin, kallikrein), matrix metalloproteinases (stromelysin, matrilysin, collagenases) and, for comparison, with trypsin and the endoproteinase Glu-C. More than 50 major cleavage sites were identified by Edman degradation of several large fragments and smaller peptides. The data show an almost exclusive localization of protease-sensitive sites to the flexible segment, connecting the N-terminal globular domains G1 and G2, and within the C-terminal, laminin-binding domain G3. Domains G1, G2 and the rod-like segment were much more stable against proteolysis. Kinetic analysis indicated a fast cleavage of several different sites in the link region followed by destruction of G3 but this was to some extent variable depending on the particular protease. Leucocyte elastase was identified as the most active protease in the cleavage of nidogen whilst stromelysin, matrilysin, plasmin and kallikrein were of distinctly lower activity. No cleavage could be detected with interstitial collagenase and gelatinase A. The peptide analyses also allowed the location of two disulfide bridges within the G3 domain. Complex formation between nidogen and laminin fragments caused some protection against cleavage by thrombin, leucocyte elastase and stromelysin particularly in domain G3. The data indicate a relatively uniform cleavage pattern of nidogen which may be relevant in the context of protein/ligand-binding activities associated with domains G2 and G3. The proteolytic processes involved in remodelling and the cellular penetration of basement membranes could therefore be essential for the modulation of the mediator function of nidogen.

Animals↗
PubMed1993

Matrix metalloproteinases cleave at two distinct sites on human cartilage link protein.

The actions of human recombinant stromelysins-1 and -2, collagenase, gelatinases A and B and matrilysin on neonatal human proteoglycan aggregates were examined. With the exception of gelatinase B, aggrecan was degraded extensively by most metalloproteinases studied, whereas link protein showed only limited proteolysis. Sequencing studies of modified link protein components revealed that stromelysins-1 and -2, gelatinases A and B and collagenase cleaved specifically between His16 and Ile17, and matrilysin, stromelysin-2 and gelatinase A cleaved between Leu25 and Leu26. Cleavage at the former bond generated a link protein component with the same N-terminus as that isolated from newborn human cartilage. Based on previously determined in situ cleavage sites it is evident that matrix metalloproteinases are not solely responsible for the accumulation of link protein degradation products in adult human cartilage, indicating that additional proteolytic agents are involved in the normal catabolism of human cartilage matrix.

Aggrecans↗
PubMed1993

Fibroblast and neutrophil collagenases cleave at two sites in the cartilage aggrecan interglobular domain.

The actions of recombinant human fibroblast collagenase (MMP1), purified polymorphonuclear leucocyte collagenase (MMP8) and their N-terminal catalytic domain fragments against cartilage aggrecan and an aggrecan G1-G2 fragment have been investigated in vitro. After activation with recombinant human stromelysin and typsin, both collagenases were able to degrade human and porcine aggrecans to a similar extent. An N-terminal G1-G2 fragment (150 kDa) was used to identify specific cleavage sites occurring within the proteinase-sensitive interglobular domain between G1 and G2. Two specific sites were found; one at an Asn341-Phe342 bond and another at Asp441-Leu442 (human sequence). This specificity of the collagenases for aggrecan G1-G2 was identical with that of the truncated metalloproteinase matrilysin (MMP7), but different from those of stromelysin (MMP3) and the gelatinases (MMP2 or gelatinase A; MMP9 or gelatinase B) which cleave at the Asn-Phe site, but not the Asp-Leu site. In addition, collagenase catalytic fragments lacking C-terminal hemopexin-like domains were tested and shown to exhibit the same specificities for the G1-G2 fragment as the full-length enzymes. Thus the specificity of the collagenases for cartilage aggrecan was not influenced by the presence or absence of the C-terminal domain. Together with our previous findings, the results show that stromelysin-1, matrilysin, gelatinases A and B and fibroblast and neutrophil collagenases cleave at a common, preferred site in the aggrecan interglobular domain, and additionally that both fibroblast and neutrophil collagenases cleave at a second site in the interglobular domain that is not available to stromelysin or gelatinases.

Aggrecans↗
PubMed1993

The 28-kDa N-terminal domain of mouse stromelysin-3 has the general properties of a weak metalloproteinase.

The putative matrix metalloproteinase mouse stromelysin-3 was expressed from Escherichia coli and from a mouse myeloma cell line. In the former case a single major protein of 58-kDa was detectable by immunoblotting, but no proteolytic activity could be elicited by zymography or trypsin or organomercurial treatment as would be expected for a typical matrix metalloproteinase. In the latter case immunodetectable proteins of 55-58 and 27-28-kDa were produced. The effect of trypsin or organomercurial treatment of the 55-58-kDa forms was to generate a 51-kDa form and lower molecular mass fragments. Upon zymographic analysis only the 27-28-kDa forms showed caseinolytic activity. N-terminal sequencing and immunoblotting analysis with antibodies specific to distinct domains of stromelysin-3 indicated that the 27-28-Da stromelysin-3 forms had lost the predicted propeptide and the majority of the C-terminal domain. The purified 28-kDa form of stromelysin-3 could weakly degrade a number of extracellular matrix proteins and was inhibited by TIMP. However, the evidence that mature full-length stromelysin-3 is a metalloproteinase could not be substantiated and the precise role of this protein in vivo remains to be elucidated. By partial analogy with interstitial collagenase, one hypothesis is that stromelysin-3 with an intact C-terminal domain has specific properties for an as yet undefined substrate.

Amino Acid Sequence↗
PubMed1993

Structural analysis of tissue inhibitor of metalloproteinases-1 (TIMP-1) by tryptic peptide mapping.

Tryptic digests of recombinant TIMP-1 have been resolved on reverse-phase HPLC and the major peaks identified by N-terminal sequencing. This procedure accounted for the entire molecule, except two short peptides of 2 and 4 amino acids in length. The peptide map was used to (i), characterize an insoluble 'core' peptide seen on digestion of TIMP-1 in non-reducing conditions; (ii), confirm the structure of delta 127-184TIMP-1, a recently described truncated form of the TIMP-1 molecule; (iii), identify exposed regions of the intact and truncated TIMP-1 molecules by measuring the rate of tryptic peptide release and (iv), locate sites of aberrant proteolysis seen when recombinant human TIMP-1 was purified at large scale.

Amino Acid Sequence↗
PubMed1993

The activity of the tissue inhibitors of metalloproteinases is regulated by C-terminal domain interactions: a kinetic analysis of the inhibition of gelatinase A.

The cloning and expression of the full-length tissue inhibitor of metalloproteinase 2 (TIMP-2), delta 187-194TIMP-2, and delta 128-194TIMP-2 and the purification of these inhibitors and a cleaved version of TIMP-2 lacking nine C-terminal amino acids (delta 186-194TIMP-2) are described. The mechanism of inhibition of gelatinase A by the TIMPs was investigated by comparing the kinetics of association of TIMP-1, TIMP-2, the C-terminal deletions, and the mutants of both TIMPs which consisted of the N-terminal domain only. The full-length TIMPs inhibited gelatinase A rapidly with association constants of 3.2 x 10(6) M-1 s-1 for TIMP-1 and 2.1 x 10(7) M-1 s-1 for TIMP-2 at I = 0.2. The C-terminal peptide of TIMP-2 is proposed to exist as an exposed "tail" responsible for binding to progelatinase A and for increasing the rate of inhibition of active gelatinase A through electrostatic interactions with the C-terminal domain of the enzyme. The C-terminal domains of both TIMP-1 and TIMP-2 participate in low-affinity interactions with the C-terminal domain of gelatinase A which increase the rate of association by a factor of about 100 in both cases.

Amino Acid Sequence↗
PubMed1993

Crystallization and preliminary X-ray analysis of a truncated tissue metalloproteinase inhibitor delta 128-194 TIMP-2.

Crystals of an active truncated form of a human tissue metallproteinase inhibitor (delta 128-194 TIMP-2), a protein implicated in a number of diseases of the connective tissues, have been grown in a form suitable for study by X-ray diffraction analysis. Crystals grow using polyethylene glycol 600 as a precipitant and are in space group P2(1)2(1)2, with cell dimensions a = 75.28 A, b = 100.77 A, c = 31.45 A. The asymmetric unit appears to contain two molecules of delta TIMP-2 with a Vm value of 2.3 A3/dalton. The crystals diffract to Bragg-spacings beyond 2.5 A. Native data to 3.2 A have been collected and a search for heavy-metal derivatives is in progress.

Crystallization↗
PubMed1993

Degradation of entactin by matrix metalloproteinases. Susceptibility to matrilysin and identification of cleavage sites.

Entactin is the basement membrane protein which bridges laminin and type IV collagen. Entactin is known to be degraded by serine proteinases, but its susceptibility to matrix metalloproteinases has not been determined. We have studied the capacity of three matrix metalloproteinases (interstitial collagenase, 92-kDa gelatinase, and matrilysin) to degrade entactin. While all three metalloenzymes cleaved entactin, matrilysin was approximately 100-fold as effective as collagenase and 600-fold as effective as 92-kDa gelatinase. The Km of matrilysin for entactin was 8.9 x 10(-7) M. A Vmax of 21 molecules of entactin degraded/molecule of matrilysin/min at 37 degrees C was observed. An Arrhenius plot relating matrilysin's catalytic activity to temperature was linear from 15 to 37 degrees C and indicated an activation energy of 10,060 calories/mol. Matrilysin produced multiple, but distinct, cleavages in entactin resulting in peptide fragments ranging from 115 to 29 kDa. The precise sites of cleavage of six fragments were determined by Edman degradation. Cleavage sites consistently occurred amino-terminal to leucine or isoleucine. These data indicate that entactin is a substrate for matrix metalloproteinases. The effectiveness of matrilysin is noteworthy, however, particularly in relation to the minimal ability of other much more well described matrix metalloproteinases to attack this substrate. Our results suggest a potentially important role for matrilysin in disruption of basement membranes by tumor or inflammatory cells.

Amino Acid Sequence↗
PubMed1993

Crystallization and preliminary X-ray analysis of nonglycosylated tissue inhibitor of metalloproteinases-1, N30QN78Q TIMP-1.

A nonglycosylated (N30QN78Q) form of the human tissue inhibitor of metalloproteinases, TIMP-1, has been prepared and crystallized in a form suitable for X-ray diffraction analysis. Small single crystals have been grown using sodium tartrate as a precipitant. The crystals are in space group P2(1), with cell dimensions a = 35.28, b = 53.95, c = 48.56, and beta = 96.0 degrees. There is a single molecule of TIMP-1 in the asymmetric unit. The crystals diffract to at least 2.3 A resolution. Complete data have been collected to 2.9 A and a search for heavy-metal derivatives is in progress.

Base Sequence↗
PubMed1993

Aminoglycoside ototoxicity in pediatric patients receiving long-term peritoneal dialysis.

We evaluated 14 children on long-term peritoneal dialysis for ototoxicity associated with aminoglycoside (AG) therapy. Baseline evaluation of all patients and 7 controls included pure-tone audiometry (PTA) and click-evoked auditory brain stem response (ABR). Nine patients had repeat PTA and ABR evaluations and vestibular testing 1 year after study entry. Five patients had an additional assessment following intraperitoneal AG therapy. The baseline auditory function of the patients was significantly poorer than controls at 6.0 and 8.0 kHz by PTA (P < 0.05), whereas the results of ABR testing were not different. Of the 14 patients, 4 (28%) had hearing loss, 3 of whom had a history of intravenous AG therapy. In contrast, none of the patients who received intraperitoneal AG therapy only, or without a history of AG therapy, had hearing loss (P < 0.005). There was no evidence of progressive loss of hearing acuity with time or associated with intraperitoneal AG therapy. One patient had findings of vestibular dysfunction. We conclude that children receiving peritoneal dialysis are at risk of AG ototoxicity. While intraperitoneal administration of AG may be associated with less ototoxicity than intravenous administration, further study is necessary to verify this finding and close monitoring of AG levels remains mandatory irrespective of the route of administration. PTA rather than click-evoked ABR appears to be the best indicator of abnormal hearing acuity in this population.

Adolescent↗
PubMed1993

Self-injurious behavior in Rett syndrome: interactions between features of Rett syndrome and operant conditioning.

Operant and biological theories of the cause of self-injurious behavior (SIB) in people with a mental handicap are often viewed as mutually exclusive. In this single case study, interactions between features of Rett syndrome and operant conditioning as determinants of SIB are examined. Functional analysis by analog methodology indicated different functions for two forms of SIB shown by the subject: automatic reinforcement by sensory stimulation and escape from social interactions. It is suggested that features of Rett syndrome established conditions under which operant conditioning of self-injurious responding was maximized. The implications of this interaction between features of syndromes and operant conditioning for the conceptualization of the cause of SIB are discussed and it is proposed that the notion of a unitary cause of SIB is inappropriate. It is more productive to consider operant conditioning as the process that maintains responding against a background of predisposing and mediating factors which may be biologically determined.

Child, Preschool↗
PubMed1993

The use of aversive stimuli in treatment: the issue of consent.

It has been argued that, in the consideration of the use of aversive stimuli in treatment, the issues are ideological and philosophical as well as technical. Adopting Horner's (1990) definition of what is meant by 'aversive' in the ideological debate, it is suggested that the crucial issue is the inability of making clients to give their informed consent. It is proposed that proxy consent might be an alternative, but that this would be unacceptable if aversive procedures could be shown to be never in the best interests of the client, or shown to violate clients' rights or to be against the interests of society because of anticipated harm or injustice to others. It is concluded that it is difficult to be certain that it is ever in the best interests of the client for aversive procedures to be employed, that aversive interventions appear not to violate clients' rights necessarily (except possibly the right to dignity and respect while the intervention is operating, and perhaps the right to choice at the beginning of the intervention), but that the inescapable difficulty in the use of aversive interventions is the likelihood that they will be misused with other clients than the ones for whom they may be initially designed.

Aversive Therapy↗
PubMed1993

Patient identifiers: stumbling blocks or cornerstones for CPRs (computer-based patient records)?

As the computer-based patient record, or CPR, moves closer to reality, patient identification issues remain unresolved. A mechanism already in place would be the Social Security number, or SSN. But legal questions surround its use for specific identification purposes. And not everyone has one. Healthcare Informatics asked several people closely involved with computerizing patient records about alternatives to social security numbers. Their responses may prove enlightening.

Computer Security↗