Biomedical subjects

N H Tan

Publications and source records attributed to N H Tan.

At least 37 records · Page 2Linked to original sources

PubMed1993

Isolation and characterization of a hemorrhagin from the venom of Calloselasma rhodostoma (Malayan pit viper).

The major hemorrhagin (termed rhodostoxin) of the venom of Calloselasma rhodostoma (Malayan pit viper) was purified to electrophoretic homogeneity by Sephadex G-200 gel filtration followed by high performance ion exchange chromatography. The purified hemorrhagin also yielded a single peak in reversed-phase HPLC. It had an isoelectric point of 5.3 and a mol. wt of 34,000. Rhodostoxin exhibited potent proteolytic, hemorrhagic and edema-inducing activities but was not lethal to mice at a dose of 6 microgram/g (i.v.). Treatment of rhodostoxin with EDTA eliminated both the proteolytic and hemorrhagic activities completely. The N-terminal sequence of rhodostoxin was determined to be NHEIKRHVDIVVVXDSRFCTK.

Amino Acid Sequence↗

PubMed1993

A comparative study on the biological properties of venoms from juvenile and adult common tiger snake (Notechis scutatus) venoms.

1. The biological properties of venoms from juvenile and adult common tiger snakes (Notechis scutatus) were compared. 2. The lethality, procoagulant activity and enzymatic activities of the juvenile venom were not substantially different from those of the adult venom. 3. Electrophoretic studies, however, indicated some minor differences in the protein composition of the juvenile and adult venoms.

Aging↗

PubMed1992

Purification and properties of the L-amino acid oxidase from monocellate cobra (Naja naja kaouthia) venom.

1. The L-amino acid oxidase of the monocellate cobra (Naja naja kaouthia) venom was purified to electrophoretic homogeneity. The molecular weight of the enzyme was 112,200 as determined by Sephadex G-200 gel filtration chromatography, and 57,400 as determined by SDS-polyacrylamide gel electrophoresis. 2. The enzyme had an isoelectric point of 8.12 and a pH optimum of 8.5. It showed remarkable thermal stability, and, unlike many venom L-amino acid oxidase, was also stable in alkaline medium. The enzyme was partially inactivated by freezing. 3. The enzyme was very active against L-phenylalanine and L-tyrosine, moderately active against L-tryptophan, L-methionine, L-leucine, L-norleucine, L-arginine and L-norvaline. Other L-amino acids were oxidized slowly or not oxidized. 4. Kinetic studies suggest the presence of a side-chain binding site in the enzyme, and that the binding site comprises of at least four hydrophobic subsites.

Amino Acid Oxidoreductases↗

PubMed1992

A comparative study of the biological properties of venoms of some old world vipers (subfamily viperinae).

1. The hemorrhagic, procoagulant, anticoagulant, phosphodiesterase, hyaluronidase, alkaline phosphomonoesterase, 5'-nucleotidase, arginine ester hydrolase, phospholipase A, L-amino acid oxidase and protease activities of 30 samples of venoms from nine species (12 taxa) of the old world vipers (Subfamily Viperinae) including snakes from the genera Bitis, Causus, Cerastes, Echis, Eristicophis and Pseudocerastes, were determined and the Sephadex G-75 gel filtration patterns for some of the venoms were also examined. 2. Examination of the biological properties of the venoms of the Viperinae tested indicates the presence of common venom biological characteristics at the various phylogenic levels. 3. Venoms of most species of the Viperinae examined exhibited characteristic biological properties at the species level, and this allows the differentiation of the Viperinae species by differences in their biological properties. 4. Particularly useful for this purpose, are the effects of venom on kaolin-cephalin clotting time of platelet poor rabbit plasma and the Sephadex G-75 gel filtration pattern and arginine ester hydrolase activity of the venom.

Animals↗

PubMed1992

The use of enzyme-linked immunosorbent assay for the quantitation of Calloselasma rhodostoma (Malayan pit viper) venom and venom antibodies.

The specificity and sensitivity of an indirect and two (an 'ordinary' and a 'rapid') double sandwich enzyme-linked immunosorbent assay (ELISA) procedures for the quantitation of Calloselasma rhodostoma (Malayan pit viper) venom were examined. The three assays were equally sensitive and the accuracy of the assays was not substantially affected by individual variation in the venom composition. The specificity of the assays was examined against 26 venoms from snakes of the families Viperidae and Elapidae. While the double sandwich ELISA procedures were sufficiently specific to be used in the clinical immunodiagnosis of C. rhodostoma bite in Malaysia, the indirect ELISA procedure exhibited extensive cross-reactivity with other Malaysian pit viper venoms. Attempts were made to improve the specificity of the indirect ELISA procedure for the quantitation of C. rhodostoma venom. A 'low ELISA cross-reactivity' venom fraction (termed VF52) was isolated from C. rhodostoma venom by repeated Sephadex G-100 gel filtration chromatography. The indirect ELISA procedure using antibodies to VF52 as immunoreagent showed an improvement in specificity. The use of the indirect ELISA procedure for the detection of C. rhodostoma antibodies was also examined and the results show that the assay was sufficiently specific to be used for retrospective diagnosis of C. rhodostoma bite in Malaysia, in particular when VF52 was used as the coating antigen.

Antibody Specificity↗

PubMed1992

The biological properties of venoms of some American coral snakes (Genus micrurus).

1. The biological properties of nine venom samples from six taxa of Micrurus were investigated. The venoms exhibited low protease, phosphodiesterase and 5'-nucleotidase activities, moderate to strong phospholipase A and hyaluronidase activities, variable L-amino acid oxidase activity and were devoid of arginine ester hydrolase and thrombin-like activities. Some venom samples exhibited strong acetylcholinesterase activity. Venoms of M. c. dumerili and M. frontalis exhibited exceptionally high alkaline phosphomonoesterase activity while two of the M. f. fulvius venom samples tested exhibited strong hemorrhagic activity in mice. 2. The polyacrylamide gel electrophoretic patterns of the venoms indicate that most of the Micrurus venom proteins are basic proteins. All Micrurus venoms tested exhibited similar SDS-polyacrylamide gel electrophoretic patterns, with an intense low mol. wt protein band. 3. The Micrurus venoms appear to exhibit biological properties similar to other elapid venoms found in Asia and Africa. There are, however, no common characteristics in the biological properties of the venoms examined at the generic level.

Animals↗

PubMed1992

A comparative study on the electrophoretic patterns of snake venoms.

1. Examination of the polyacrylamide gel electrophoretic (PAGE) and SDS-PAGE patterns of snake venoms shows that these patterns are useful for species differentiation (and hence identification) for snakes of certain genera but have only limited application for snakes from some other genera, due either to the marked individual variations in the venoms or the lack of marked interspecific differences within the same genus. 2. There is no substantial intersubspecific difference in the electrophoretic patterns of the venoms. 3. In general there are no common characteristics in the electrophoretic patterns of the venom at the generic level because of the wide variations in the electrophoretic patterns of venoms of snakes within the same genus. 4. At the familial level, the venoms of Elapidae exhibited SDS-PAGE patterns distinct from those of Crotalidae.

Animals↗

PubMed1992

The biological properties of venoms from juvenile and adult taipan (Oxyuranus scutellatus) snakes.

1. The biological properties of four venom pooled samples from adult taipan (Oxyuranus scutellatus) snakes and one pooled venom sample from six juvenile taipan snakes (11 months old) were compared. 2. The intravenous LD50 (median lethal dose), procoagulant activity and enzymatic activities of the juvenile venom were not significantly different from those of the adult venoms. 3. The juvenile and adult venoms exhibited similar polyacrylamide gel electrophoretic (PAGE) and SDS-PAGE patterns, indicating that they possessed a similar protein composition. 4. The results suggest that there is no significant age-dependency in the biological properties of taipan venom.

Age Factors↗

PubMed1992

Comparative study of the enzymatic, hemorrhagic, procoagulant and anticoagulant activities of some animal venoms.

1. The enzymatic, hemorrhagic, procoagulant and anticoagulant activities of venoms of some animals including snakes, lizards, toads, scorpions, spider, wasps, bees and ants were compared. 2. Snake venom was the richest source of enzymes among the animal venoms. Most other animal venoms were devoid of phosphodiesterase, L-amino acid oxidase, alkaline phosphomonoesterase and acetylcholinesterase activities and only a few exhibited arginine ester hydrolase activity. These venoms, however, exhibited wide ranges of protease, 5'-nucleotidase and hyaluronidase activities. Most of the animal venoms examined exhibited some phospholipase A activity. 3. Other than snake venoms, only venoms of the toad Bufo calamita and the lizards were hemorrhagic, and only venoms of the social wasps, social bees and harvester ant exhibited strong anticoagulant activity. Procoagulant activity occurs only in snake venoms.

Amphibian Venoms↗

PubMed1991

Substrate specificity of king cobra (Ophiophagus hannah) venom L-amino acid oxidase.

1. Substrate specificity of purified king cobra (Ophiophagus hannah) venom L-amino acid oxidase was investigated. 2. The enzyme was highly specific for the L-enantiomer of amino acid. Effective oxidation of L-amino acid by the enzyme requires the presence of a free primary alpha-amino group but the alpha-carboxylate group is not as critical for the catalysis. 3. The enzyme was very active against L-Lys, L-Phe, L-Leu, L-Tyr, L-Tryp, L-Arg, L-Met, L-ornithine, L-norleucine and L-norvaline and moderately active against L-His, L-cystine and L-Ileu. Other L-amino acids were oxidized slowly or not oxidized. 4. The data suggest the presence of a side chain binding site in the enzyme, and that the binding site comprises at least five 'subsites': the hydrophobic subsites a, b and c; and the two 'amino' binding subsites d and e. Subsite b appears to be able to accommodate two methylene/methyl carbons.

Amino Acid Oxidoreductases↗

PubMed1991

A comparative study of the biological properties of some sea snake venoms.

1. The protease, phosphodiesterase, alkaline phosphomonoesterase, L-amino acid oxidase, acetylcholinesterase, phospholipase A, 5'-nucleotidase, hyaluronidase, arginine ester hydrolase, procoagulant, anticoagulant and hemorrhagic activities of ten samples of venoms from seven taxa of sea snakes were examined. 2. The results show that venoms of sea snakes of both subfamilies of Hydrophiinae and Laticaudinae are characterized by a very low level of enzymatic activities, except phospholipase A activity and, for some species, hyaluronidase activity. 3. Because of the low levels of enzymatic activities and the total lack of procoagulant and hemorrhagic activities, venom biological properties are not useful for the differentiation of species of sea snakes. Nevertheless, the unusually low levels of enzymatic activities of sea snake venoms may be used to distinguish sea snake venoms from other elapid or viperid venoms.

5'-Nucleotidase↗

PubMed1991

A comparative study of the biological properties of some venoms of snakes of the genus Bothrops (American lance-headed viper).

1. The hemorrhagic, procoagulant, anticoagulant, phosphodiesterase, alkaline phosphomonoesterase, 5'-nucleotidase, hyaluronidase, arginine ester hydrolase, phospholipase A, L-amino acid oxidase and protease activities of 26 samples of venoms from 13 species of Bothrops were determined, and the Sephadex G-75 gel filtration patterns for some of the venoms also examined. 2. The results show that while there are considerable individual variations in the biological activities of many of the Bothrops venoms tested, there are some common characteristics at the genus and species levels. 3. The differences in the biological properties of the Bothrops venoms tested can be used for the differentiation of most Bothrops species examined.

Animals↗

PubMed1991

A comparative study of the biological activities of rattlesnake (genera Crotalus and Sistrurus) venoms.

1. The hemorrhagic, procoagulant, anticoagulant, protease, arginine ester hydrolase, phosphodiesterase, alkaline phosphomonoesterase, 5'-nucleotidase, hyaluronidase, phospholipase A and L-amino acid oxidase activities of 50 venom samples from 20 taxa of rattlesnake (genera Crotalus and Sistrurus) were examined. 2. The results show that notwithstanding individual variations in the biological activities of Crotalus venoms and the wide ranges of certain biological activities observed, there are some common characteristics at the genus and species levels. 3. The differences in biological activities of the venoms compared can be used for differentiation of the species. Particularly useful for this purpose are the thrombin-like enzyme, protease, arginine ester hydrolase, hemorrhagic and phospholipase A activities and kaolin-cephalin clotting time measurements.

Acetylcholinesterase↗

PubMed1991

A comparative study of the biological properties of Dendroaspis (mamba) snake venoms.

1. The biological properties of twelve samples of venoms from all four species of Dendroaspis (mamba) were investigated. 2. Dendroaspis venoms generally exhibited very low levels of protease, phosphodiesterase and alkaline phosphomonoesterase; low to moderately low level of 5'-nucleotidase and very high hyaluronidase activities, but were devoid of L-amino acid oxidase, phospholipase A, acetylcholinesterase and arginine ester hydrolase activities. The unusual feature in venom enzyme content can be used to distinguish Dendroaspis venoms from other snake venoms. 3. All Dendroaspis venoms did not exhibit hemorrhagic or procoagulant activity. Some Dendroaspis venoms, however, exhibited strong anticoagulant activity. The intravenous median lethal dose of the venoms ranged from 0.5 microgram/g mouse to 4.2 micrograms/g mouse. 4. Venom biological activities are not very useful for the differentiation of the Dendroaspis species. The four Dendroaspis venoms, however, can be differentiated by their venom SDS-polyacrylamide gel electrophoretic patterns.

Animals↗

PubMed1991

The edema inducing activity of phospholipase A2 enzymes.

The edema inducing activity of phospholipase A2 (PLA2) enzymes from snake venoms and porcine pancreas was investigated using mouse paw as experimental model. All ten PLA2 enzymes exhibited potent edema inducing activity. PLA2, however, is generally not the major edema inducing component of snake venom. Chemical modification studies indicated that enzymatic activity of PLA2 was required for its edema inducing activity. All PLA2 enzymes examined displayed a rapid onset edema which was suppressed by pretreatment of the mice with antihistamine. Dexamethasone pretreatment also inhibited edemas elicited by some PLA2 enzymes.

Animals↗

PubMed1990

Purification and characterization of two acidic phospholipase A2 enzymes from king cobra (Ophiophagus hannah) snake venom.

1. The two major phospholipase A2 enzymes (OHPLA-DE1 and OHPLA-DE2) of king cobra (Ophiophagus hannah) venom have been purified to electrophoretic homogeneity. 2. The isoelectric points of OHPLA-DE1 and OHPLA-DE2 were 3.81 and 3.89, respectively and the Mws were 14,000 and 15,000, respectively, as estimated by Sephadex G-75 gel filtration chromatography; and 14,000 as estimated by SDS-PAGE. 3. The enzymes were not lethal to mice at a dosage of 10 micrograms/g body wt by i.v. route. Both phospholipase A2 enzymes, however, exhibited moderate edema-inducing and anti-coagulant activities. 4. Bromophenacylation of the enzymes reduced the enzymatic activity drastically but did not affect the edema-inducing activity of the enzymes.

Acetophenones↗

PubMed1990

Isolation and characterization of a hemorrhagin from the venom of Ophiophagus hannah (king cobra).

The major hemorrhagin (termed hannahtoxin) of the venom of Ophiophagus hannah (king cobra) was purified to electrophoretic homogeneity by DEAE-Sephacel ion exchange chromatography, Sephadex G-200 gel filtration followed by a second DEAE-Sephacel chromatography. Proteolytic activity was associated with the hemorrhagic activity throughout the purification procedures. Hannahtoxin constituted approximately 2% of the crude venom. It had an isoelectric point of 5.3, a carbohydrate content of 12%, a mol. wt of 66,000 as determined by SDS-polyacrylamide gel electrophoresis and 63,000 as determined by gel filtration. It contains 1 mole of Zn per mole of protein. The minimum hemorrhage doses for hannahtoxin are 0.7 microgram and 75 micrograms, respectively, in rabbits and in mice. Hannahtoxin was not lethal to mice at a dose of 2 mg/kg (i.v.) but killed rabbits at doses above 0.18 mg/kg (i.v.). It liberated protein from rabbit glomerular basement membrane but not rat glomerular basement membrane. Treatment of the hemorrhagin with EDTA and 1,10-phenanthroline eliminated both the proteolytic and hemorrhagic activities completely.

Animals↗

PubMed1990

Preparation of antibodies to king cobra (Ophiophagus hannah) venom hemorrhagin and investigation of their cross-reactivity.

Hannahtoxin, the major hemorrhagin purified from king cobra (Ophiophagus hannah) venom, elicits hemorrhages in rabbits but not in mice. Two antisera against hannahtoxin were prepared: one raised against purified hannahtoxin, while the other was raised against glutaraldehyde cross-linked and detoxified hannahtoxin. The antisera were refined by pepsin digestion and ammonium sulfate precipitation. They are of approximately equal potency in their ability to neutralize the hemorrhagic activity of king cobra venom in rabbits. The antisera did not form a precipitin line with venom of snakes of the Viperidae family nor neutralize hemorrhages elicited in mice by any of these venoms. However, when the hemorrhagic activity was assayed in rabbits, both antisera were able to abolish the hemorrhages elicited by all of the venoms tested. These results suggest that hannahtoxin displays few epitopes in common with hemorrhagins of viperid venoms, except those involved in the neutralization of hemorrhagic activity in rabbits. The epitopes of viperid venom hemorrhagins involved in the neutralization reaction in rabbits are different from those in mice.

Animals↗