M. Alkazaz et al., THE MECHANISM OF PORCINE PANCREATIC ALPHA-AMYLASE - INHIBITION OF MALTOPENTAOSE HYDROLYSIS BY ACARBOSE, MALTOSE AND MALTOTRIOSE, European journal of biochemistry, 252(1), 1998, pp. 100-107
A kinetic study was carried out on the inhibitory effects of acarbose,
maltose, and maltotriose on porcine pancreatic cx-amylase (PPA), usin
g maltopentaose as the substrate. Lineweaver-Burk plots showed that th
e inhibitory action of acarbose is of the mixed non-competitive type.
The secondary plots gave straight lines. A model involving abortive co
mplexes accounts for these results. Dixon plot analysis led to the sam
e conclusion. According to the proposed model, one molecule of acarbos
e per amylase molecule binds either directly to free enzyme at the act
ive site or to the enzyme-substrate complex at a secondary carbohydrat
e-binding site, which becomes functional after the substrate has bound
to the enzyme molecule at the active site. Kinetic analysis of the in
hibition exerted by either the maltose or maltotriose reaction product
s of maltopentaose hydrolysis were then performed. The inhibitory effe
ct of maltose was found to be of the non-competitive type, while that
of maltotriose was competitive. It can therefore be concluded that the
first reaction product to be released upon maltopentaose hydrolysis i
s maltose, and that the second product is maltotriose. This indicates
that after hydrolysis of the maltopentaose chain, the reducing side fr
agment is released first.