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Biomedical subjects

N H Tan

Publications and source records attributed to N H Tan.

63 records · Page 4Linked to original sources
PubMed1986

Enzymatic activities of Calloselasma rhodostoma (Malayan pit viper) venom.

The enzyme contents of four venom samples of Calloselasma rhodostoma were analyzed. The venoms contained phosphodiesterase, alkaline phosphomonoesterase, 5'-nucleotidase, protease, phospholipase A, L-amino acid oxidase, hyaluronidase, arginine ester hydrolase, arginine amidase, fibrinogenase and coagulant enzyme activities. There is significant variation in the contents of coagulant enzyme, arginine ester hydrolase, hyaluronidase, protease, phosphodiesterase, alkaline phosphomonoesterase and L-amino acid oxidase. DEAE-Sephacel ion exchange chromatography of the venom resolved it into eight major protein fractions. The eight fractions were heterogeneous and exhibited more than one type of enzymatic activity. The 5'-nucleotidase, alkaline phosphomonoesterase, protease, coagulant enzyme, arginine ester hydrolase, arginine amidase and fibrinogenase exist in multiple forms.

Aminopeptidases↗
PubMed1983

Isolation and characterization of two toxins from the venom of the Malayan cobra (Naja naja sputatrix).

Two principal toxins of the Malayan cobra (Naja naja sputatrix) venom have been purified to electrophoretic homogeneity by successive SP-Sephadex C-25 ion exchange chromatography and Sephadex G-50 gel filtration chromatography. They are designated as sputa-neurotoxin 1 (SN1) and sputa-neurotoxin 2 (SN2), respectively. both toxins belong to the group of short neurotoxins which are composed of approximately 60 amino acid residues. The LD50 values following i.p. injection of the purified toxins are 91 (SN1) and 71 (SN2) micrograms/kg mouse. Amino acid compositions of the two toxins show close similarities to other postsynaptically acting curaremimetic cobra neurotoxins.

Amino Acids↗
PubMed1983

Improvement of Malayan cobra (Naja naja sputatrix) antivenin.

A low molecular weight toxic fraction was isolated from venom of the Malayan cobra (Naja naja sputatrix) by Sephadex G-50 gel filtration chromatography. The fraction accounted for almost 100% of the venom lethality. Antisera were prepared by immunizing rabbits with the low molecular weight toxic fraction, the glutaraldehyde-treated low molecular weight toxic fraction and the glutaraldehyde-treated, sea snake neurotoxin-enriched low molecular weight toxic fraction, respectively. Only the serum of rabbits immunized with the glutaraldehyde-treated, neurotoxin-enriched fraction gave effective protection against high doses of Malayan cobra venom. This antiserum is thus a potent Malayan cobra antivenin. One milliliter of this antiserum was able to neutralize 1.5 mg of Malayan cobra venom. It is thus 4-8 times more potent than the commercially available Malayan cobra antivenins produced by immunizing horses with whole Malayan cobra venom.

Animals↗
PubMed1982

Isolation and preliminary characterisation of two toxic phospholipases A2 from the venom of the Malayan cobra (Naja naja sputatrix).

Two toxic phospholipases A have been isolated from the venom of the Malayan cobra (Naja naja sputatrix). The phospholipases A were purified by successive ion-exchange chromatography on SP-Sephadex C-25, Sephadex G-75 gel filtration chromatography and successive Bio-Rex 70 ion-exchange chromatography. The purified toxic phospholipases A were homogeneous electrophoretically. They were designated as sputatrix phospholipase A-I and sputatrix phospholipase A-II. Positional specificity studies showed that they belong to the A2-type phospholipase A. The medium lethal dose 50% (LD50) values of the two phospholipases A are 0.27 and 0.28 microgram/g, respectively, by intravenous injection and 1.05 and 1.00 microgram/g, respectively, by intraperitoneal injection. The molecular weights of the two enzymes are 14000 as determined by gel-filtration chromatography and SDS-polyacrylamide gel electrophoresis. Amino acid composition of sputatrix phospholipase A-I differs from sputatrix phospholipase A-II only by having one extra amino acid: a glutamic acid. Amino acid compositions of the two enzymes are also similar to those of other cobra venom phospholipases A.

Amino Acids↗
PubMed1982

Acidic phospholipases A2 from the venom of common sea snake Enhydrina schistosa.

Two acidic phospholipases A have been purified from the venom of common sea snake (Enhydrina schistosa) by chromatography on Sephadex G-75 gel media, Bio-Rex 70 ion-exchanger followed by repeated Chromatography on DEAE-Sephadex A-25 ion-exchanger. The two preparations were shown to be homogeneous by polyacrylamide gel electrophoresis and ion-exchange chromatography. The enzymes were shown to be specific for the 'two' position of egg yolk lecithin. The molecular weight of both enzymes determined by gel filtration chromatography and SDS-polyacrylamide gel electrophoresis was approx. 14 000. Both enzymes were non-lethal. Amino acid composition data indicated high contents of aspartic acid, glycine and alanine in both enzymes.

Amino Acids↗
PubMed1977

Synthesis and characterization of a pancreatic trypsin inhibitor homologue and a model inhibitor.

The synthesis and characterization of protein proteinase inhibitor homologues with variations in the amino acid composition in the vicinity of the reactive site should aid the understanding of the mechanism by which inhibition of enzymatic activity occurs. A homologue inhibitor in which the reactive-site residue Ala-16 of basic pancreatic trypsin inhibitor (Kunitz) (BPTI) is replaced by Phe has been synthesized to study the effect of this replacement on the dissociation constants of the enzyme-inhibitor complexes. The replacement of Ala-16 by Phe causes a dramatic increase in the K1 value of the trypsin-BPTI complex while that of the chymotrypsin-BPTI complex remains essentially the same. This cannot be explained simply in terms of increased steric crowding. The Phe replacement probably causes a small change in the local conformation of the reactive site of the inhibitor which leads to a large decrease in the stability of the very tight trypsin-BPTI complex. This conformation change apparently can be tolerated in the less tightly bound chymotrypsin-BPTI complex. On the basis of the known structure of BPTI, a cyclic heptadecapeptide containing one disulfide bond was synthesized as a model inhibitor in order to determine if a smaller peptide can be designed to act as a highly efficient inhibitor for trypsin. This heptadecapeptide which contains all of the amino acid residues of BPTI taking part in the interaction of the proteinase inhibitor with trypsin binds 3 X 10(7) time more weakly to the enzyme than native BPTI does. It thus appears that even though only a small part of the inhibitor molecule enters directly into interaction with the enzyme, the remaining portions of the molecule which hold the structure of the inhibitor rigid are essential for the strong interaction.

Amino Acid Sequence↗