I= STUDIES ON INHIBITION OF ACETYCHOLINESTERASE OF VERTEBRATES BY ORGANOPHOSPHORUS INSECTICIDES ACETYLCHOLINESTERASE OF GOAT BRAIN
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Title of Thesis
STUDIES ON INHIBITION OF ACETYCHOLINESTERASE OF VERTEBRATES BY ORGANOPHOSPHORUS INSECTICIDES ACETYLCHOLINESTERASE OF GOAT BRAIN

Author(s)
Akbar Ali Cheema
Institute/University/Department Details
Department of Zoology University of the Punjab Lahore
Session
1987
Subject
Zoology
Number of Pages
255
Keywords (Extracted from title, table of contents and abstract of thesis)
ACETYCHOLINESTERASE VERTEBRATES, ORGANOPHOSPHORUS INSECTICIDES, ACETYLCHOLINESTERASE, GOAT BRAIN, malaoxon, anti-cholinesterase activity, Organophosphate structure, Carbamate structure

Abstract
In the biochemical characterization of acetylcholinesterase of goat brain the enzymic activity was found to reside primarily in the particulate fraction of the homogenate. The Michaselis 5.71x10-1, and maximum velocity was 27 micromoles of acetylcholine hydrolyzed per 0.1 ml of the homogenate per minute. The enzymic activity was accelerated between pH 5.8 and 6.5 and then increased gradually up to pH 8.0. The optimum temperature ranged between 30-50oC. Hydrolysis of acetylcholine was inhibited by manganese sulphate and lead chloride but activated by calcium chloride, cadmium nitrate and magnesium sulphate.

Inhibition of acetylcholinesterase by malaoxon was found to be progressive in nature. 0.65x10-4 malaoxon caused 100% inhibition of the enzymic activity in an incubation period of about two hours whereas a concentration of 2.62 x 10-4 M malaoxon was and the reaction was, therefore, a bimolecular one. The bimolecular rate constant was 2.6 x 102 liters Mole-1. Maximum inhibition was noticed at pH 8.0 found to be 11.4 Kcal. Mole-1.

Reactivation of maloxon-inhibited acetylcholinesterase by PAM-2- Could not be detected with Hestrin technique at pH 7.38 and at 17,27 and 37oC. This failure for to detect any reactivation was due to inhibition of the enzyme by the reactivator itself. Lower concentrations of PAM-2 failed to yield any reactivation even after an incubation period of twelve hours at 32oC. Reactivation of the enzyme could not be demonstrated could not be used.

Inhibition of acetylcholinesterase with PAM-2 increased with increase in the concentration of the inhibitor. I50 was approximately 3mM with homogenate concentration from 0.25 to 1.0ml. The residual activity in the presence of PAM-2 at pH 7.38 increased with an increase in the concentration of the substrate. This indicated that PAM-2 was a reversible and competitive inhibitor of goat brain acetylcholinesterase. Inhibition was also found to be a function of pH.

7.7x 10-6 M concentration of physostigmine sulfate inhibition 100% acetylcholinesterase activity. I50 of the inhibitor was around 3x10-7. Inhibition of the enzyme by different concentrations of eserine was not reversed when the concentration of the substrate was increased from 1 to 4mM. Inhibition was, however, found to be dependent upon pH, with maximum at pH 6.0
Download Full Thesis
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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
82.65 KB
2 1 General Introduction 1
4288.96 KB
  1.1 Mode of action of organophosphates 1
  1.2 Organophosphate structure and anti-cholinesterase activity 4
  1.3 Carbamate structure and anti-cholinesterase activity 9
  1.4 Selective toxicity and ch8ilinestereae activity 10
3 2 Review of literature 19
362.59 KB
  2.1 Discovery, substrate specificity and nomenclature of cholinesterase 19
  2.2 Distribution of cholinesterases 26
  2.3 Active centre of acetylcholinesterase 28
  2.4 Inhibitors of cholinesterases 33
  2.5 Kinetics and mechanism of inhibition by organophosphates 36
  2.6 Mechanism of cholinesterase inhibition by carbamates 43
  2.7 Spontaneous reactivation of phorylated and carbamyated cholinesterases 49
  2.8 Kinetics and mechanism of reactivation (in vitro ) 54
  2.9 Aging 60
  2.10 Therapy 62
  2.11 Protection 66
4 3 Aim of the study 71
423.66 KB
5 4 Experimental studies 71
680.92 KB
  4.1 Biochemical characterization of acetylcholinesterase of goat brain 72
  4.2 Kinetics of inhibition of acetylcholinesterase of goat brain by Malaoxon 100
  4.3 Studies on reactivation by pyridine-2-Alodxime methiodide (PAM-2) on Malaoxon-Inhibited acetylcholinesterase of goat grain 123
  4.4 Inhibition of goat brain acetylcholinesterase by physostigmine (Eserine ) 150
6 5 References 177
394.01 KB
7 6 Appendix 220
446.66 KB
  6.1 Research publications