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Biomedical subjects

M Chang

Publications and source records attributed to M Chang.

At least 163 records · Page 9Linked to original sources
PubMed1987

Histone H2B repression causes cell-cycle-specific arrest in yeast: effects on chromosomal segregation, replication, and transcription.

To determine which cellular processes are dependent on histones, we blocked histone H2B mRNA synthesis in asynchronously growing yeast after fusing the H2B gene to a repressible GAL10 promoter. Chromosomal segregation, replication, and transcription were then examined. We found that the cells arrested in mitosis, with a cell division cycle (cdc) phenotype. Chromatin structure and nuclear segregation were disrupted. A full round of DNA replication took place after the repression of histone H2B mRNA synthesis. Active transcription and the induction of new transcripts also continued in the arrested cells.

Cell Cycle↗
PubMed1987

Enzymatic transformation of PGH2 to PGF2 alpha catalyzed by glutathione S-transferases.

Glutathione S-transferases (GSTs) purified from both rat liver cytosol and microsomes catalyzed the direct reduction of PGH2 to PGF2 alpha. As much as 40% of the substrate was transformed into a prostanoid whose Rf value corresponded to that of PGF2 alpha. The identification of the reaction product as PGF2 alpha was confirmed by TLC and reverse-phase HPLC as well as by mass spectral analysis. In the absence of GSTs, PGH2 was found to be primarily converted to PGE2 and PGD2. Also, PGF2 alpha formation was completely abolished by decylglutathione, a potent inhibitor of both peroxidase and transferase activity associated with GSTs. These results indicate that the direct reduction of endoperoxide moiety of PGH2 to form PGF2 alpha is an enzymatic process. Interestingly, selenium-dependent glutathione peroxidase (Se-GSH-Px) showed very little PGF2 alpha formation from PGH2. However, this enzyme was very active in the reduction of PGG2 to PGH2. In contrast, GSTs were very poor in the conversion of PGG2 to PGH2. Therefore, it is possible that the relative tissue distribution of Se-GSH-Px and GSTs might play an important role in the tissue specific synthesis of PGF2 alpha.

Animals↗
PubMed1987

Specificity of the glutathione S-transferases in the conversion of leukotriene A4 to leukotriene C4.

We have synthesized the 5,6-LTA4, 8,9-LTA4, and 14,15-LTA4 as methyl esters by an improved biomimetic method with yields as high as 70-80%. We have investigated the catalytic efficiency of the purified cytosolic glutathione S-transferase (GST) isozymes from rat liver in the conversion of these leukotriene epoxides to their corresponding LTC4 methyl esters. Among various rat liver GST isozymes, the anionic isozyme, a homodimer of Yb subunit, exhibited the highest specific activity. In general, the isozymes containing the Yb subunit showed better activity than the isozymes containing the Ya and/or Yc subunits. Interestingly, all three different LTA4 methyl esters gave comparable specific activities with a given GST isozyme indicating that regiospecificity of GSTs was not the factor in determining their ability to catalyze this reaction. Surprisingly, purified GSTs from sheep lung and seminal vesicles showed little activity toward these leukotriene epoxides, indicating a lack of the counterpart of rat liver anionic GST isozyme in these tissues.

Animals↗
PubMed1987

Isozyme specificity of rat liver glutathione S-transferases in the formation of PGF2 alpha and PGE2 from PGH2.

When prostaglandin H2 (PGH2) was incubated with a mixture of glutathione S-transferases (GSTs) obtained from S-hexylglutathione affinity chromatography, as much as 40% of it was transformed into a prostanoid whose Rf value corresponded to that of the standard PGF2 alpha. The reaction product was identified as PGF2 alpha by cochromatography with a standard on TLC and HPLC. The stereochemistry of the hydroxyl groups on C-9 and C-11 of the cyclopentane ring was confirmed by mass-spectral analysis of the butylboronate derivative of the reaction product. Neither PGE2 nor PGD2 could substitute for PGH2 in the reaction mixture, indicating that the mechanism of formation of PGF2 alpha is a direct two-electron reduction of the endoperoxide moiety and not through a reduction of the keto group on PGE2 or PGD2. Individual GST isozymes exhibited distinct differences in their catalytic rates of formation of PGF2 alpha from PGH2. Among various GSTs, isozyme IV, a homodimer of Ya size subunit showed the highest activity with a Vmax value of approximately 6000 nmol.min-1.mg-1. In general, the isozymes containing Ya and Yc subunits exhibited relatively high activity toward PGH2, indicating that it is the non-selenium-dependent glutathione peroxidase activity associated with the GSTs that might be responsible for the reduction of PGH2 to PGF2 alpha. Interestingly, isozyme IV also exhibited the highest PGE2 forming activity with a Vmax value of approximately 3000 nmol.min-1.mg-1 followed by isozyme I, a homodimer of Yb subunit, which had a Vmax value of 420 nmol.min-1.mg-1. Based on these results, it appears that the GSTs play an important role in the biosynthesis of classical PGs. Therefore, it is conceivable that the tissue-specific formation of PGF2 alpha and PGE2 might, in part, be due to the relative distribution of these enzyme activities in a given tissue. Our results have not only confirmed the previously published reports (E. Christ-Hazelhof et al. (1976) Biochim. Biophys. Acta 450, 450-461), but also have characterized the specificity of GST isozymes in the formation of PGF2 alpha.

Animals↗
PubMed1987

Load transfer characteristics of the wrist. Part I. The normal joint.

A static positioning frame allows the positioning of unembalmed human upper extremities in any combination of wrist flexion/extension, radio/ulnar deviation, and pronation/supination. Pressure-sensitive film (Fuji) was used to study the contact areas, scaphoid-lunate area ratios, average high pressures, centroid positions, and intercentroid distances of five wrist joints under a uniform load of 103 Newtons (N) in 36 different positions. The contact areas accounted for only 20.6% of the available joint surface. They shift from a primarily palmar location to a primarily dorsal location when the wrist changes from flexion to extension. Overall the scaphoid contact area was 1.47 times that of the lunate and was generally greatest with the wrist in ulnar deviation. The scapho-lunate contact area ratio increased as wrist position changed from radial to ulnar deviation and/or from flexion to extension. For the constant load of 103 Newtons the high pressure averaged 3.17 megapascals (MPa). The scaphoid and lunate high pressure centroids shifted palmar when wrist position changed from 20 degrees of flexion to 20 degrees of extension and then shifted dorsal with further extension of the wrist. The intercentroid distance averaged 14.91 mm and ranged from 10 to 20 mm.

Biomechanical Phenomena↗
PubMed1987

Load transfer characteristics of the wrist. Part II. Perilunate instability.

An experimental model with a static positioning frame, pressure-sensitive film (Fuji), and a microcomputer-based video digitizing system, previously developed by the two senior authors, was used in this study to examine the effects of increasing perilunate instability on the load transfer characteristics of the wrist. These effects included a significant dorsal ulnar shift of the scaphoid centroid with increasing perilunate instability together with a less dramatic palmar ulnar shift of the lunate centroid. Overall, the scaphoid contact area was found to decrease as the stage of perilunate instability increased, even in ulnar deviation and/or extension, which in the normal wrist was found to be the positions that had the greatest scaphoid contact area. Average pressures in the high pressure zones were found to significantly increase in wrists with a stage III instability compared with normal wrists. An increase in the intercentroid (scaphoid/lunate) distance was most evident with the wrist in 20 degrees extension, neutral radioulnar deviation, and 90 degrees supination.

Biomechanical Phenomena↗
PubMed1987

Phase II studies of single-agent cimetidine and the combination N-phosphonacetyl-L-aspartate (NSC-224131) plus L-alanosine (NSC-153353) in advanced malignant melanoma.

We conducted parallel phase II trials of cimetidine as a single agent and the combination N-phosphonacetyl-L-aspartate (PALA) plus L-alanosine among 40 previously untreated patients with biopsy-proven, measurable disseminated malignant melanoma. We did not design the trial to be a comparative assessment of the two regimens. Among 19 patients treated with cimetidine, 300 mg orally four times daily, there was one complete response of extensive pleural and pulmonary metastases for 16+ months and two partial regressions of soft tissue lesions for 7 and 21+ months, respectively. Among 21 patients treated with the combination regimen, there was only one partial response in soft tissue for 1 month. The median times to progression and death were 1.4 and 6 months, respectively, for cimetidine, and 1.3 and 4 months, respectively, from the combination of PALA plus L-alanosine. Among patients who progressed on initial treatment, there were no responses in 12 who received crossover therapy with cimetidine and 11 with the combination regimen. Two patients treated with the combination program had severe stomatitis, two developed renal failure, and one had severe leukopenia and thrombocytopenia. Recognizing the limitations of small sample size, these early observations suggest that cimetidine may have intriguing implications in the management of disseminated malignant melanoma.

Alanine↗
PubMed1986

Human prothymosin alpha: amino acid sequence and immunologic properties.

Prothymosin alpha has been purified from human thymus and its amino acid sequence determined, except for a 15 amino acid segment including 10 glutamyl residues near the middle of the molecule. Like prothymosin alpha from rat thymus [A. A. Haritos, R. Blacher, S. Stein, J. Caldarella, and B. L. Horecker (1985) Proc. Natl. Acad. Sci. USA 82, 343-346], human prothymosin contains the thymosin alpha 1 sequence at its NH2-terminus. It contains a total of 109-110 residues compared to 111-112 for rat prothymosin alpha, with deletions corresponding to positions Gln39 and Lys108 of the rat polypeptide. Human prothymosin alpha also differs from rat prothymosin alpha at positions corresponding to residues 87, 92, and 102 of the latter, with substitutions of alanine for proline, alanine for valine, and aspartic acid for glutamic acid, respectively. Human prothymosin is significantly less active than rat prothymosin in protecting mice against infection with Candida albicans and in stimulating release in vivo of migration inhibitory factor. Thus, the differences in amino acid sequences, present mainly the COOH-terminal half of the polypeptides, may determine species specificity in biological properties.

Amino Acid Sequence↗
PubMed1986

The primary structure of rat parathymosin.

Parathymosin has been isolated from rat thymus and from rat liver. Its primary structure is reported as follows: (Sequence; see text). The blocking group at the NH2 terminus was identified by mass spectrometry as acetyl. Regions homologous to amino acid sequences in prothymosin alpha were found to be located between residues 14-20, 23-25, 33-39, 41-43, and 83-87 of parathymosin.

Amino Acid Sequence↗
PubMed1986

Cholecystokinin-associated COOH-terminal peptides are fully sulfated in pig brain.

A radioimmunoassay was developed to detect the cholecystokinin (CCK)-associated nonapeptide (CAP-9) that forms the COOH terminus of pig preproCCK. This peptide (Ser-Ala-Glu-Glu-Tyr-Glu-Tyr-Thr-Ser) is presumably produced at the time that the tyrosine-sulfated octapeptide CCK8(s) is cleaved from preproCCK. Radioimmunoassay of a dried methanol extract of pig brain revealed no detectable CAP-9 immunoreactivity, whereas acid desulfation of the dried methanol extract prior to radioimmunoassay resulted in easily measurable concentrations of CAP-9 immunoreactivity. Two peptides, CAP-9 and des-Ser9-CAP-9, were purified from a methanol extract of 8 kg of commercially obtained whole pig brains. Amino acid analysis showed that each peptide has both tyrosines sulfated. Thus, the likely sequence of CCK post-translational processing events is sulfation of the three tyrosines in the COOH terminus of preproCCK followed by peptide cleavage and appearance of CCK8(s) and CAP-9(s,s).

Amino Acid Sequence↗
PubMed1986

Clinicopathologic correlation of ocular and neurologic findings in AIDS: case report.

The protean ocular manifestations of patients with the acquired immunodeficiency syndrome (AIDS) have been well documented both clinically and histopathologically. Since 1978, many case reports have emphasized the opportunistic ocular infections in patients with AIDS. We report the clinicopathologic findings in a patient with AIDS who demonstrated focal necrosis of the ciliary processes and cerebellum due to cytomegalovirus (CMV). The former explained the clinical manifestations of uveitis and the latter masqueraded as drug toxicity.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Acquisition of gamma camera and physiological data by computer.

We have designed, implemented, and tested a new Research Data Acquisition System (RDAS) that permits a general purpose digital computer to acquire signals from both gamma camera sources and physiological signal sources concurrently. This system overcomes the limited multi-source, high speed data acquisition capabilities found in most clinically oriented nuclear medicine computers. The RDAS can simultaneously input signals from up to four gamma camera sources with a throughput of 200 kHz per source and from up to eight physiological signal sources with an aggregate throughput of 50 kHz. Rigorous testing has found the RDAS to exhibit acceptable linearity and timing characteristics. In addition, flood images obtained by this system were compared with flood images acquired by a commercial nuclear medicine computer system. National Electrical Manufacturers Association performance standards of the flood images were found to be comparable.

Humans↗
PubMed1985

Guinea pig "little" gastrin is a hexadecapeptide.

Gastrin heptadecapeptides (gastrins I and II which differ in the presence of sulfate on the tyrosine of the latter) have been purified and sequenced from several mammalian species including pig, dog, cat, sheep, cow, human and, more recently, rat. This report describes the purification of "little" gastrin from guinea pig (GP) antra. GP antra were defatted with acetone and the acetone cakes were extracted with 0.1M NH4HCO3. The extract was concentrated by adsorption to DE53 anion exchange cellulose and the peak eluates were fractionated on a Sephadex G50F column. The peptides were brought to final purity by 3 successive HPLC steps. The GP sequence compared to other species is shown: (formula: see text) Thus GP "little" gastrins I and II are hexadecapeptides due to a deletion of a glutamic acid in the region 6-9 from the N-terminus.

Amino Acid Sequence↗
PubMed1985

Purification of dog VIP from a single animal.

VIP, a potent vasodilator peptide, is reported to be identical in pig, cow, human and rat but to differ in four amino acids in chicken. This report describes the purification of dog VIP from the small intestine of a single animal. The purification method is based on tissue extraction with a sequence of organic solvents. The extracted VIP is concentrated onto cation-exchange cellulose and brought to purity by three HPLC steps. A 30% final yield of pure VIP was obtained from the original extract. Dog VIP was found to have the following sequence: His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Thr-Arg-Leu-Arg-Lys-Gln-Met-Ala -Val-Lys-Lys-Tyr-Leu-Asn-Ser-Ile-Leu-Asn. Thus the amino acid sequence of dog VIP is identical with all the mammalian VIP's which have been reported. This suggests that a high degree of conservation throughout the molecule may be required for VIP bioactivity.

Amino Acid Sequence↗
PubMed1985

Guinea pig has a unique mammalian VIP.

Mammalian vasoactive intestinal peptide (VIP) has been reported to be identical in four species. This report describes the extraction of guinea pig (GP) intestinal VIP, its purification and sequence. Frozen intestines were extracted in five volumes of methanol and the methanol cakes reextracted with acid. VIP in the acid extract was concentrated onto ion-exchange cellulose and was brought to final purity through a series of HPLC steps. GP VIP differs from other mammalian VIP's by four amino acid substitutions: (sequence in text) This is further evidence that the GP gastroenteropancreatic axis has a unique evolutionary separation from other mammals.

Amino Acid Sequence↗