Deviation from Michaelis-Menten kinetics for esterase E-II from the venom of Bitis gabonica, using synthetic arginine amides as substrates

Nanostructuring Biomaterials with Specific Activities towards Digestive Enzymes for Controlled Gastrointestinal Absorption of Lipophilic Bioactive Molecules

This review describes the development of novel lipid-based biomaterials that modulate fat digestion for the enhanced uptake of encapsulated lipophilic bioactive compounds (e.g. drugs and vitamins). Specific focus is directed towards analysing how key material characteristics affect the biological function of digestive lipases and manipulate lipolytic digestion. The mechanism of lipase action is a complex, interfacial process, whereby hydrolysis can be controlled by the ability for lipase to access and adsorb to the lipid-in-water interface. However, significant conjecture exists within the literature regarding parameters that influence the activities of digestive lipases. Important findings from recent investigations that strategically examined the interplay between the interfacial composition of the lipid microenvironment and lipolysis kinetics in simulated biophysical environments are presented. The correlation between lipolysis and the rate of solubilisation and absorption of lipophilic compounds in the gastrointestinal tract (GIT) is detailed. Greater insights into the mechanism of lipase action have provided a new approach for designing colloidal carriers that orally deliver poorly soluble compounds, directly impacting the pharmaceutical and food industries.

A steady-state kinetic analysis of the reaction between arginine esterase E-I from Bitis gabonica venom and synthetic arginine substrates and the influence of pH, temperature and solvent deuterium isotope

1. Using synthetic arginines as substrates, steady-state kinetic studies showed a deviation from Michaelis-Menten kinetics for esterase E-I purified from the venom of Bitis gabonica. Graphical analysis indicated a rate equation of at least a degree of 3:3. 2. pH variation of the kinetic parameters indicated the involvement of groups with pK values of approximately 7 and approximately 9 which had to be in the ionic form for activity. 3. Solvent isotope studies suggested transition states where proton transfer or reorganization was the rate-limiting step of proteolytic catalysis. A single protogenic site was postulated. 4. Temperature effects on the enzymic reaction showed a significant reduction in entropy loss upon formation of the transition state with both esters and extended tail polypeptide-anilides in comparison with the activation entropy for benzoyl-L-arginine p-nitroanilide.

The Gaboon viper (Bitis gabonica): its biology, venom components and toxinology

The Gaboon viper has acquired an impressive reputation which is at least partly unfounded. This handsome animal with such striking features is undoubtedly docile which accounts for the very low incidence of bite amongst humans. There are only six detailed clinical reports on the effect of bite and these are summarized in the review. The viper does indeed produce prodigious amounts of venom, but the toxicity, weight for weight, is rather low compared to other poisonous snakes. Venom extractions have been carried out on four snakes over a 13-year-period and the effects of this venom have been studied in a variety of experimental animals. Systemic envenomation is characterized by immediate abrupt hypotension, subsequent cardiac damage and dyspnoea. The individual venom components responsible for these effects have not been isolated but it seems likely that the two enzymes which have been studied extensively (phospholipase A2 and the thrombin-like enzyme, gabonase) do not contribute significantly to lethality. We propose three principal activities which give rise to the major signs of systemic envenomation. Haemorrhagin; causing widespread damage to microvasculature which leads to the pulmonary oedema and hence dyspnoea, and locally causes blistering. Cardiotoxin; a long-acting material causing cardiac muscle damage, arrhythmia and ultimately cardiac failure. Peripheral vasodilator; a short acting effect, operating either locally via bradykinin formation and/or unknown peptides or centrally on the vasomotor centre.