The activation of bee venom phospholipase A2

Drainas, Denis (1978) The activation of bee venom phospholipase A2. PhD thesis, University of Glasgow.

Abstract

The kinetic behaviour of Bee venom phospholipase A2 was studied using both long and short chain substrates in the presence and absence of organic solvents. The activity was controlled by a variety of activators and in particular the behaviour in dilute organic solvents was dominated by fatty acid activation. The enzyme was activated irreversibly by a variety of acylating agents derived from long-chain fatty acids. The most effective derivatives were azides and imidazolides and the reactivity was proportional to the hydrocarbon chain length, in contrast to the general chemical reactivity. Oleoyl and linoleoyl imidazolide were shown to be the most effective activators and the oleoyl derivative gave full activation corresponding to addition of one acyl residue per protein molecule. Studies of maximally activated enzyme showed that earlier models in which activation was proposed to rely on fatty acid modification of the substrate surface could be ruled out. Activation does not appear to be due to modification of the rate at which the enzyme penetrates the substrate surface but it is sensitive to the physico-chemical properties of the substrate. A model is proposed whereby allosteric activation of the enzyme is communicated to the active site of the protein by an interaction involving the acyl side chains of the substrate. Activation is calcium dependent and at low calcium concentrations the activation factors exceed 100-fold. Furthermore the same experiments produced evidence that the enzyme has two sites for calcium and the activation by acylating agents substitutes the second weakly reactive calcium. The covalently activated enzyme causes lytic damage to the rabbit erythrocytes where the unactivated enzyme has very little effect. Therefore this type of activation could be of importance in vivo.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: A J Lawrence
• Keywords: Biochemistry
• Date of Award: 1978
• Depositing User: Enlighten Team
• Unique ID: glathesis:1978-72391
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 24 May 2019 15:12
• Last Modified: 24 May 2019 15:12
• URI: https://theses.gla.ac.uk/id/eprint/72391