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Biomedical subjects

P K Tsung

Publications and source records attributed to P K Tsung.

At least 19 recordsLinked to original sources
PubMed1985

Identification of low-Ca2+- and high-Ca2+-requiring neutral proteases in rat retina.

Two low-Ca2+-requiring proteases (calpain I) and one high-Ca2+-requiring protease (calpain II) have been separated from the cytosol of rat retina by DEAE-cellulose column chromatography. Calpain I was half-maximally activated at 3 microM free Ca2+ and fully activated at 10 microM free Ca2+. Half-maximal activation of calpain II was at 0.4 mM free Ca2+ while full activation was observed at 0.8 mM free Ca2+. Calpain activity has also been demonstrated in sealed rod outer segments. The soluble fraction of the rod outer segments contained 89% of the enzyme activity. The possible role of calpain in retina is discussed.

Animals↗
PubMed1985

Cathepsin B and D, and Ca2+-dependent neutral protease activities in the retina of taurine-depleted rats.

Rats were treated with guanidinoethanesulfonic acid (GES), a taurine transport inhibitor, which reduces the tissue content of taurine. The quantity of taurine in the rat retinas after GES treatment was reduced by 46% after the first week, 60% after the second week, and 67% after the third week. Activities of cathepsin B and D were not significantly altered when calculated on the basis of either protein or DNA content in the taurine-depleted retinas. However, cytosolic Ca2+-dependent neutral protease activity in retinas from GES-treated rats increased by 55% after the third week.

Animals↗
PubMed1985

Identification and partial purification of a nucleotide-stimulated protease in rat retina.

A nucleotide-stimulated protease of rat retina was partially purified by DEAE-cellulose column chromatography. A 50-fold increase of an ATP-stimulated protease activity over a cytosol fraction was achieved by this chromatography. Maximum stimulation of protease activity by ATP was achieved at 2 mM. The pH optimum of the ATP-stimulated protease activity was between 7.5 and 8.5. 2 mM GTP stimulated the protease activity by 91%. 5 mM cyclic AMP stimulated the protease activity by 73% while 5 mM cyclic GMP stimulated the activity by 84%. The possible role of the nucleotide-stimulated protease in retina and potential involvement of the protease with inherited retinal dystrophy are discussed.

Adenosine Diphosphate↗
PubMed1984

Intracellular distribution and properties of cathepsin B in the rat retina and its inhibition by a cytosolic fraction.

The intracellular distribution and properties of cathepsin B in the rat retina are similar to those of cathepsin B in other mammalian tissues. The specific activity of cathepsin B was highest in the mitochondrial-lysosomal fraction [1650 +/- 450 pmole mg-1 protein hr-1 (mean +/- S.D.)]. Inhibition of cathepsin B activity by a cytosol fraction of retina is also described.

Animals↗
PubMed1983

Decrease of lactoferrin concentration in the tears of myotonic muscular dystrophy patients.

Tears from myotonic muscular dystrophy (MMD) patients and normal controls were analyzed for their tear proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lactoferrin comprised about 18% of the total tear protein in MMD patients as opposed to about 27% in normals. The albumin content relative to total protein in MMD tears was about 25% while the same value for normals is 13%. The lactoferrin/albumin ratio, was about 0.8 for MMD patients and about 2.1 for normals.

Erythrocyte Membrane↗
PubMed1983

Changes in lysosomal enzyme activities of eye tissues in endotoxin-induced inflammation.

Lysosomal enzyme activities in rabbit ocular tissues were examined at various times after the intravitreal injection of endotoxin. Lysosomal enzyme activities in the aqueous, vitreous, and pigment epithelium-choroid were elevated 3 h after injection. It is deduced from the fluorescein-labeled dextran and SDS-polyacrylamide gel electrophoresis analysis of the aqueous, vitreous, and pigment epithelium-choroid from endotoxin injected rabbits that the elevation of lysosomal enzyme activities are probably due to a breakdown in blood-ocular barriers.

Acid Phosphatase↗
PubMed1981

Protease activities in human tears.

Several protease activities were measured in human tears by six specific substrates. The specific activity of cathepsin B-like enzyme was 7-fold higher in Orientals than in Caucasians. The trypsin-like and cathepsin C-like enzyme activities also showed 3 to 4-fold higher in Orientals than in Caucasians. However, the deviation in the activities of these two enzymes was high in both Orientals and Caucasians. Similar results were obtained when comparing the protease activities of tear collected by glass capillary and a filter-paper strip method. Since a surface-active small molecular weight fraction can be produced by incubation of freshly collected tears for 4 hours at 37 degrees C, the low molecular weight surfactant may be a proteolytic product.

Asian People↗
PubMed1980

Surface membrane enzyme, chemotactic peptide binding activities, and chemotactic responsiveness of rabbit peripheral and peritoneal neutrophils.

The chymotrypsin-like esterase activity of plasma membrane and the ecto-5'nucleotidase and ecto-p-nitrophenyl phosphatase activities in peritoneal neutrophils are 2- and 3-fold higher than peripheral blood neutrophils. The binding of the chemotactic peptide, formyl norleucyl-leucyl-phenyl-alanine to peritoneal neutrophils is 6- to 7-fold higher than to peripheral blood neutrophils. The chemotactic responsiveness of peritoneal neutrophils to the chemotactic peptide is 5-fold greater than peripheral blood neutrophils. However, there was no significant difference in the chemotactic responsiveness to complement component C5a between the blood and peritoneal cells.

Animals↗
PubMed1978

The evidence for the existence of chymotrypsin-like esterase activity in the plasma membranes of rabbit neutrophils and the specific chemotactic peptide binding activity of the subcellular fractions.

1. Light- and heavy-plasma membrane fractions have been isolated from rabbit neutrophils and a chymotrypsin-like esterase has been shown to be present in these fractions. 2. The molecular weight of the chymotrypsin-like esterase of rabbit neutrophil plasma membrane was estimated to be about 200 000. 3. About 93% of the chymotrypsin-like esterase of the plasma membranes is esterase 1 and the susceptibility to potential inhibitors was similar in light- and heavy-plasma membrane. 4. Chemotactic peptide, [3H]formyl-norleucyl-leucyl-phenylalanine [3H]formyl-Nle-Leu-Phe) binding by subcellular fractions shows that the highest specific binding was observed in the light-plasma membrane was about 2-fold higher than the heavy-plasma membrane, about 37-fold higher than the nuclear fraction, about 3-fold higher than lysosomal fraction and about 10-fold higher than the microsomal fraction.

Animals↗
PubMed1976

Chemotactic activity from rabbit peritoneal neutrophils. Lack of identity with N-acetyl-DL-phenylalanine beta-napthyl esterase.

The chemotactic and N-acetyl-DL-phenylalanine beta-naphthyl esterase activities of rabbit peritoneal neutrophils are separable from each other by both DEAE cellulose and Sephadex G-100 column chromatography. Partially purified esterase obtained from DEAE-cellulose chromatography had molecular weight of 70 000. However, the partially purified fraction contained chemotactic activities with major activity in molecular weight of 28000 and minor activities in the molecular weights of 45000, 21900, 14500 and 10500. Esterase activity is inhibited by 10(-7) M p-nitrophenylethyl-5-chloropentylphosphonate but chemotactic activity is not.

Aminopeptidases↗
PubMed1975

Formation of phagolysosomes containing dextran and Triton WR 1339 in mouse liver.

After injection of Triton WR 1339 and dextran into mice, phagolysosomes containing both compounds were obtained from the liver regardless of the order of injection of these materials. This suggests that phagososomes containing the other material. The recoveries of various lysosomal enzymes differed in phagolysosomes after injection of Triton WR 1339 with or without dextran: recoveries of beta-glucuronidase, beta-N-acetylglucosaminidase and arylsulfatase were high, and that of acid phosphatase was low.

Acetylglucosamine↗
PubMed1975

Protein kinase and phosphatases from human polymorphonuclear leucoytes.

Purified preparations of human polymorphonuclear leucocytes contain a protein kinase in the cytosol which is stimulated by cyclic AMP and cyclic IMP but not by other cyclic nucleotides. The holoenzyme had a molecular weight of 66000 estimated by gel filtration; when it was incubated with histone or cyclic AMP, it dissociated into two smaller subunits of molecular weight 45000 and 30000; the former remained cyclic AMP-sensitive, whereas the latter had become independent of added cyclic AMP. By means of substrate-affinity chromatography on histone-Sepharose 4B, cyclic [3H5AMP-binding activity (regulatory or R subunit) could be resolved into two peaks of enzyme activity, one again independent of added cyclic AMP, with a molecular weight of 30000 (catalytic or C subunit). Also by means of substrate-affinity chromatography it was possible to resolve 'specific' polymorphonuclear leukocyte histone phosphatases from 'non-specific' phosphomonesterases capable of dephosphorylating histone previously phosphorylated by the protein kinase. Specific histone phosphatase displayed greatest affinity for histone-Sepharose 4B, followed by acid p-nitrophenyl phosphatase, and the unretained acid beta-glucerophosphatase. Polymorphonuclear leucocyte histone phosphatase, purified approx. 40-fold, was further resolved from the other phosphatases by gel filtration on Sephadex G-150 from which it was eluted with apparent molecular weights of 45000 and 18700. The apparent Km values for dephosphorylation of histone are 4.3 X 10-6M and 3.6 X 10-6M. Most (69%) of cytoplasmic histone phosphatase was found in the cell sap, whereas 20% remained tightly associated with polymorphonuclear leucocyte lysosomes from which it could not be solubilized by treatments (Triton X-100, freeze-thawing) that released approx. 70% of lysosomal beta-glucuronidase or acid phosphatases. Although both soluble and particulate enzymes required 5-10 mM-Mn2 for maximal activation, and showed a pH maximum of 6.5-7.0, only the particulate enzyme was partly inhibited by ammonium molybdate. Polymorphonuclear leucocyte histone phosphatases were neither inhibited nor stimulated by those cyclic nucleotides that greatly stimulate the protein kinase of the same subcellular fraction

Acid Phosphatase↗