Introduction: Soursop (Annona muricataLinn) is an edible lowland
tropical fruit-bearing tree that is widely cultivated across regions of the
world. It has been extensively researched as a result of its store of
acetogenin; a potent anticancer agent. However, there is a dearth of
information on the precise mechanism of action of acetogenin. It is
therefore imperative to investigate this plant in the hope of discovering a
different class of anticancer agent inherent in it. Various studies have
demonstrated that cysteine protease inhibitors (CPIs) have considerable
therapeutic potential which can be utilized in a variety of disease states
including cancer.
Aims: Study was designed to isolate, purify and characterize CPI from
the fruits and seeds of Soursop.
Materials and Methods:Isolation and purification of CPI were achieved
by simple methods consisting of ammonium sulphate precipitation, anion
exchange chromatography and size exclusion chromatography. Mode of
inhibition, optimum pH and temperature, as well as the effect of metals
on the enzyme activity was determined using spectrophotometry.
Results:The purified CPI from seeds and fruits exhibited competitive and
noncompetitive inhibition against papain respectively. However, maximal
inhibitory activities for both fruit and seed samples were observed at
similar optimal pH and temperature of 8 and 40°C respectively. Although,
metal cations such as cobalt (Co2+), copper (Cu2+) and zinc (Zn2+) did not
impact a considerable decrease on the inhibitory activity of the CPI; Lead
(Pb2+), Magnesium (Mg2+) and manganese (Mn2+) significantly inhibited
CPI at a very low concentration (1mM).
Conclusion: The antagonistic properties exhibited by the purified CPI
certainly indicate its likely suitability for pharmaceutical application in the
treatment of some pathological conditions such as cancer, in which
uncontrolled proteolytic activities of cysteine proteases are implicated.
There is an ample scope for further research on structure elucidation and
protein engineering to facilitate its usage in a wide range of application.