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Biomedical subjects

M K Cha

Publications and source records attributed to M K Cha.

14 recordsLinked to original sources
PubMed1999

Ceruloplasmin has a distinct active site for the catalyzing glutathione-dependent reduction of alkyl hydroperoxide.

Ceruloplasmin, a blue multi-copper alpha(2)-glycoprotein found in the plasma of all vertebrates, is capable of oxidizing aromatic amines and ferrous iron. Here, we report that human ceruloplasmin exhibits an alkyl hydroperoxide peroxidase activity, which is independent of the oxidase activity. The site-specific modification of the sulfhydryl of cysteine at position 699 in ceruloplasmin completely abolished the antioxidant activity, suggesting that ceruloplasmin is a peroxidase with a cysteinyl thiol as a functional nucleophile. The crystal structure of human ceruloplasmin reveals that the domain containing Cys-699 is apart from the multi-copper complex domains. Taken together, these data suggest that ceruloplasmin has a distinct active site for a glutathione-linked peroxidase activity apart from the copper complex site exerting ferroxidase activity.

Antioxidants↗
PubMed1998

Effect of prolonged subcutaneous implantation of peritoneal catheter on peritonitis rate during CAPD: a prospective randomized study.

We conducted a prospective randomized controlled study to confirm our earlier observation that prolonged subcutaneous implantation of peritoneal catheter reduced peritonitis rate when compared to retrospective data from patients with catheters placed by conventional access technique. A total of 60 patients were randomized into two groups: 30 patients had catheters left implanted subcutaneously for 6 weeks (I) and the other 30 patients had catheters inserted by conventional technique and had 6 weeks of break-in period (C). Subgroups of 15 patients each with new and conventional techniques used Y-connector (IY, CY) and remaining patients used standard spikes (IS, CS). Mean age was 47.7 years (range 16-71); 61.0% were male and 44.1% diabetics. Peritonitis, exit site infection, simultaneous peritonitis and exit site infection, and complication related to Staphylococcus or Pseudomonas infections were observed for up to 2 years in each patient after initiation of bag exchange or until termination of CAPD by transfer to hemodialysis or by death. Total duration of observation was 493.2 patient-months for new access technique and 409.6 patient-months for conventional technique. Patients in IY group had the lowest incidence of peritonitis (1/14.9 patient-months) and exit site infection (1/16.8 patient-months) among four subgroups. Peritonitis rate in IY was significantly lower compared to CY or CS. The total peritonitis-free period in those patients who did not experience peritonitis during the observation period was also significantly longer in IY (120 patient-months) than in CY (26 patient-months), IS (10.6 patient-months), or CS (10.4 patient-months). Simultaneous peritonitis and exit site infection was observed in none of IY group but 3 episodes in CY, 4 episodes in IS, and 3 episodes in CS. The rates of complications related to Staphylococcus aureus and Pseudomonas infections were also significantly lower in IY than in CY, IS, or CS. Technique survival did not differ between the two groups. The present results confirm our previous observation that the new access technique reduces the incidence of peritonitis probably by reducing infection via periluminal route. The Y-connector system further reduces peritonitis rate by reducing infection via intraluminal route.

Adolescent↗
PubMed1996

Glutathione-linked thiol peroxidase activity of human serum albumin: a possible antioxidant role of serum albumin in blood plasma.

A 65-kDa molecular mass of thiol-specific antioxidant protein was purified from human plasma and identified as human serum albumin (HSA) by the analysis of amino-terminal amino acid sequence. This protein exhibited the preventive effects against the inactivation of glutamine synthetase activity and the peroxidation of lipid by a metal-catalyzed oxidation system. These antioxidant activities were supported by a thiol-reducing equivalent such as DTT and reduced glutathione. The thiol-specific antioxidant activity of HSA was greatly activated by halide ion, especially by chloride ion. HSA showed a significant capability to destroy H2O2 in the presence of reduced glutathione, resulting in the production of oxidized glutathione. Both the preventive activity against the glutamine synthetase inactivation and the peroxidase activity were completely abolished by the reactions of HSA with N-ethylmaleimide and iodoacetate, chemical modification agents for sulfhydryl of protein, only in the presence of thiol-reducing equivalent such as DTT. These results suggest that serum albumin acts as a major and predominate antioxidant exerting a glutathione-linked thiol peroxidase activity which removes reactive oxygen species such as H2O2 within blood plasma.

Amino Acid Sequence↗
PubMed1996

Identification of promoter in the 5'-flanking region of the E. coli thioredoxin-linked thiol peroxidase gene: evidence for the existence of oxygen-related transcriptional regulatory protein.

E. coli thiol peroxidase (Tpx) linked to the thioredoxin as an in vivo thiol regenerating system acts as an antioxidant enzyme removing peroxides and H2O2. In order to elucidate the mechanism regulating tpx gene expression in E. coli in response to oxygen stress, we made 5' progressive deletions of upstream region from tpx gene, and fused to lacZ gene. LacZ activity was increased 6-fold by oxygen stress and inverted repeat sequence located between -47 and -33 nt was proven to be essential for the oxygen response of tpx promoter. Primer extension experiment and analysis of upstream sequence revealed transcription start point, -10, and -35 regions, which are in good agreements with the consensus sequences recognized by E sigma 70. Northern hybridization showed that expression of tpx gene is regulated at the transcriptional level. DNA binding assays using inverted repeat sequence including -35 region provides preliminary evidence that expression of tpx requires additional transcriptional factor in response to oxygen stress.

Amino Acid Sequence↗
PubMed1996

Mutation and Mutagenesis of thiol peroxidase of Escherichia coli and a new type of thiol peroxidase family.

A novel thioredoxin-linked thiol peroxidase (Px) from Escherichia coli has been reported previously (M. K. Cha, H. K. Kim, and I. H. Kim, J. Biol. Chem. 270:28635-28641, 1995). In an attempt to perform physiological and biochemical characterizations of the thiol Px, a thiol Px null (tpx) mutant and a functional-residue mutant of thiol Px were produced. The tpx mutant was viable in aerobic culture but grew more slowly than the wild-type cells. The difference in growth rate became more pronounced when oxidative-stress-inducing reagents, such as peroxides and paraquat, were added to the cultures. The viability of the individual tpx mutant under oxidative stress was much lower than that of wild-type cells. tpx mutants growing aerobically respond to paraquat with a sixfold greater induction of Mn-superoxide dismutase than that of the wild-type cells. The deduced amino acid sequence of the thiol Px was found to be from 42 to 72% identical to the sequences of proteins from Haemophilus influenzae (ToxR regulon), Vibrio cholerae (ToxR regulon), and three kinds of streptococci (coaggregation-mediating adhesins), suggesting that they all belong to a new thiol Px family. Alignment of the amino acid sequences of the thiol Px family members showed that one cysteine, which corresponds to Cys-94 in E. coli thiol Px, is perfectly conserved. The substitution of serine for this cysteine residue resulted in complete loss of Px activity. These results suggest that the members of the thiol Px family, including E. coli thiol Px, have a functional cysteine residue and function in vivo as peroxidases.

Amino Acid Sequence↗
PubMed1996

Dialysis in patients with diabetic nephropathy: CAPD versus hemodialysis.

Diabetic nephropathy has emerged as a major cause of ESRD over the past decade, being the most prevalent cause of ESRD requiring dialysis in North America (United States and Canada) and the second highest in the incidence rate in Europe, Japan, Korea, Australia, and New Zealand. A greater proportion of older patients and of patients with diabetic nephropathy and other comorbid conditions has been treated with CAPD. Despite the preferential use of CAPD to treat a high-risk group of patients, the overall and/or selection-adjusted mortality was similar between HD and CAPD groups. Among diabetic patients, selection-adjusted mortality was similar between HD and CAPD or lower in CAPD than in HD, the difference being greatest among younger patients and significant through the age of 52, or higher in CAPD than in HD with higher risk of death for older diabetics (age > or = 50 years), but with similar risk among younger diabetics (age < 50 years). Technique survival was also variably reported as similar between HD and CAPD, lower, or higher with CAPD compared to HD. Diabetic CAPD patients had more hospital admissions and more days in the hospital and higher withdrawal rates from dialysis compared to diabetic HD patients. These disparate results of patient and technique survival between HD and CAPD in diabetic patients may have resulted from patient selection criteria with different comorbid conditions on entrance to dialysis, quantity of dialysis, and other unrecognized factors. Prospective randomized studies are needed to assign a cause-and-effect relationship between the choice of dialysis modality and patient and technique survival among patients with diabetes mellitus as well as with all other diagnostic categories.

Diabetic Nephropathies↗
PubMed1995

Thioredoxin-linked peroxidase from human red blood cell: evidence for the existence of thioredoxin and thioredoxin reductase in human red blood cell.

A thiol-dependent antioxidant protein (HRPRP) was previously reported as a predominant antioxidant protein in human red blood cell (RBC). The analysis of amino acid sequence of HRPRP with those of human PRP-like gene products indicates that HRPRP is identical to brain PRP (HPRP). This protein act as a peroxidase linked to thioredoxin (Trx)/thioredoxin reductase (TR). Until now, there was no evidence for Trx/TR system in RBC. The existence of the Trx/TR system in RBC was immunologically determined. A 58-kDa protein showing TR activity was partially purified from human RBC and characterized. Our results reveal that HRPRP act as a new type of peroxidase supported by Trx/TR system in human RBC.

Amino Acid Sequence↗
PubMed1995

Thioredoxin-linked "thiol peroxidase" from periplasmic space of Escherichia coli.

Three different molecular masses (24, 22, and 20 kDa) of antioxidant proteins were purified in Escherichia coli. These proteins exhibited the preventive effects against the inactivation of glutamine synthetase activity and the cleavage of DNA by a metal-catalyzed oxidation system capable of generating reactive oxygen species. Their antioxidant activities were supported by a thiol-reducing equivalent such as dithiothreitol. Analysis of the amino-terminal amino acid sequences and the immunoblots between 24- and 22-kDa proteins indicates that the 24-kDa protein is an intact form of the 22-kDa protein that was previously identified 22-kDa subunit (AhpC) of E. coli alkyl hydroperoxide reductase (AhpC/AhpF). We isolated and sequenced an E. coli genomic DNA fragment that encodes 20-kDa protein. Comparison of the deduced amino acid sequence of the 20-kDa protein with that of AhpC revealed no sequence homology. A search of a data bank showed that the 20-kDa protein is a new type of antioxidant enzyme. The synthesis of this novel 20-kDa protein was increased in response to oxygen stress during growth. The 20-kDa protein resides mainly in the periplasmic space of E. coli, whereas the 24-kDa AhpC resides mainly in the matrix. The 20-kDa protein was functionally linked to the thioredoxin as an in vivo thiol-regenerating system and exerted a peroxidase activity. This 20-kDa protein is thus named "thiol peroxidase," which could act as an antioxidant enzyme removing peroxides or H2O2 within the catalase- and peroxidase-deficient periplasmic space of E. coli.

Amino Acid Sequence↗
PubMed1994

The thiol-specific antioxidant protein from human brain: gene cloning and analysis of conserved cysteine regions.

The complete cDNA encoding human thiol-specific antioxidant protein (PRP) was isolated from a human brain cDNA library in the lambda Zap expression vector. An open reading frame (ORF) was identified and found to encode a polypeptide of 197 aa with a M(r) of 21,729. The cDNA contained 98 bp of 5'-untranslated sequence (UTR) and 259 bp of 3'-UTR containing a poly(A) signal, AATAAA. Expression of the human PRP cDNA in Escherichia coli yielded a functionally active protein. The observed local sequence homologies between human PRP and other homologous proteins whose functions have not yet been defined give important insight into elucidating the biochemical function of a new protein family which has highly conserved regions containing cysteine.

Amino Acid Sequence↗
PubMed1994

Purification and characterization of thiol-specific antioxidant protein from human red blood cell: a new type of antioxidant protein.

A thiol-specific antioxidant protein (Protector Protein, PRP) was purified from human red blood cells (RBC). The PRP exists as a predominant protein in human RBC, which showed distinct thiol-specific antioxidant activities in the presence of dithiothreitol (DTT) as a reducing equivalent. The human RBC PRP (HRPRP) completely inhibited visible absorption spectral changes of oxyhemoglobin, DNA cleavage, and the peroxidation of RBC membrane by a nonenzymatic Fe3+/O2/thiol mixed-function oxidation system capable of generating hydroxyl radical. These observations suggest that HRPRP could act as a new type of antioxidant protein to maintain the RBC integrity by scavenging reactive oxygen species.

Antioxidants↗
PubMed1993

Removals of hydrogen peroxide and hydroxyl radical by thiol-specific antioxidant protein as a possible role in vivo.

Thiol-specific antioxidant protein (Protector Protein; PRP) from Saccharomyces cerevisiae was found to remove hydrogen peroxide and hydroxyl radical in the presence of dithiothreitol (DTT). Without DTT as a reducing equivalent, the antioxidant protein did not show the activities for destroying hydrogen peroxide and hydroxyl radical. N-ethylmaleimide (NEM) was observed to prevent the PRP from both removing hydrogen peroxide and protecting the cleavage of DNA. These observations suggest that the sulfhydryl of cysteine in PRP could function as a strong nucleophile to attack and destroy H2O2 and .OH.

Antioxidants↗