I= STUDIES ON THE INHIBITION OF PROTEASES, TYROSINASE AND RELATED ENZYMES BY NATURAL PRODUCTS AND SYNTHETIC COMPOUNDS
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Title of Thesis
STUDIES ON THE INHIBITION OF PROTEASES, TYROSINASE AND RELATED ENZYMES BY NATURAL PRODUCTS AND SYNTHETIC COMPOUNDS

Author(s)
Usman Ghani
Institute/University/Department Details
University of Karachi/ H.E.J. Research Institute of Chemistry
Session
2001
Subject
Chemistry
Number of Pages
212
Keywords (Extracted from title, table of contents and abstract of thesis)
proteases, tyrosinase, enzymes, synthetic compounds, serine proteinase, polypeptide trypsin

Abstract
Proteinases play key roles in various physiological processes. However, excessive activity of proteinases leads to many diseases such as cancer, emphysema, bronchitis, arthritis, etc. Controlling or inhibiting the excessive proteolysis is an important step in treating various diseases. Similarly various diseases and clinical conditions such as hyper pigmentation, nevus a potential in controlling such ailments. A variety of natural and synthetic proteinase and tyrosinase inhibitors have potential commercial value, they can be developed and utilized as fruit-browning inhibitory agents and as safer insecticides

In this work a number of new mechanism-based inhibitors of tyrosinase and chymotrypsin have been studied kinetically and structurally including some protein serine proteinase inhibitors. Chymotrypsin inhibitors such as analogues of meta and para benzoates and tyrosinase inhibitors such as defivatives of 1,3,4-thiadiazole and substituted hydrazides have been studied with their structure-activity relationship deduced. X-ray crystallographic methods were also utilized to determine the structure of chymotrypsin in complex with 7-hydroxycounarin and its mechanism of inhibtion

Earlier studies indicate that the amino acid sequence of the inhibitor-II (TI-II) from tomato leaves has a two-domain organization. The sequence has two repeats, with each repeat containing one reactive loop located near the N-terminus of the repeat. Attempts were made to crystallize the TI-II in order to determine the crystal structure by molecular replacement and isomorphous replacement methods using a proposed search model of TI-II. The TI-II search model gave an approximate idea about the overall fold of the molecule and how the sequence repeats give rise to a two-domain organization and their association with each other

A remarkable aspect of the canonical inhibitors of serine proteinases is that most of the enzyme binding loops of the members of the 18 families of serine proteinase inhibitors superpose well despite their different global structure. Interaction of the binding loops of TI-II and the polypeptide trypsin inhibitors with trypsin and chymotrypsin is in close agreement with that of the canonical inhibitors of serine proteinases as indicated by molecular modeling studies

Download Full Thesis
1481.21 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents 0
88.05 KB
2 1 General Introduction 1
354.45 KB
  1.1 Serine Proteinase 1
  1.2 Tyrosinase 22
  1.3 Comparative Molecular Modeling 31
3 2 Screening & Kinetic Studies Of Serine Proteinase And Tyrosinase Inhibitors 46
352.51 KB
  2.1 Introduction 46
  2.2 Materials And Methods 59
  2.3 Results & Discussion 62
  2.4 Conslusions 92
4 3 Crystal Structure Of 7-Hydroxycoumarin In Complex With Y-Chymotrypsin 95
233.58 KB
  3.1 Introduction 95
  3.2 Materials And Methods 97
  3.3 Results & Discussion 101
  3.4 Conslusions 121
5 4 Comparative Molecular Modeling Of Polypeptide Trypsin Inhibitors And Construction Of Ti-Ii Search Model For Molecular Replacement Studies 123
307.39 KB
  4.1 Introduction 123
  4.2 Materials And Methods 126
  4.3 Results & Discussion 129
  4.4 Conclusions 161
6 5 Crystallization And X-Ray Data Analysis Of Proteinase Inhibitor-Ii From Tomato Leaves 163
396.3 KB
  5.1 Introduction 163
  5.2 Materials And Methods 166
  5.3 Results & Discussion 171
  5.4 Conclusions 185
  5.5 References 187