Interaction of Antipsychotic Drugs with Sucrase, Kinetics and Structural Study

In patients with the Congenital Sucrase-Isomaltase Deficiency (CSID), who lack intestinal sucrase-isomaltase enzyme, a suspension of yeast sucrase is applied as a drug to compensate the enzyme deficiency. While antipsychotic drugs are used for the treatment of schizophrenia, administering multiple drugs at the same time may counteract each other.

In this study, the interaction between trifluoperazine and haloperidol as antipsychotic drugs on oral drug yeast sucrase was investigated. In this regard, the kinetic parameters of enzyme were determined in the presence or absence of the drugs. The kinetic parameters of the drugs such as Ki and IC50 were also calculated. Lineweaver - Burk plot was used to reveal the type of inhibition.

The results showed that both drugs could reduce sucrase activity and decrease the Vmax of the enzyme by non-competitive inhibition. The IC50 and Ki values of the drugs were determined to be 0.7 and 0.068 mM and 0.45 and 0.063 mM for haloperidol and trifluoperazine, respectively. The results suggested that trifluoperazine binds to the enzyme with higher affinity than haloperidol. Fluorescence measurement was used for conformational investigations of the drugs and sucrase interaction. It was shown that the drugs bind to free enzyme and enzyme-substrate complex which are accompanied with hyperchromicity. This suggests that tryptophan residues of the enzyme transferred to hydrophobic medium after binding of the drugs to the enzyme.

The finding of this research revealed that both trifluoperazine and haloperidol could inhibit sucrase in non-competitive manner. The kinetic parameters and conformational changes due to binding of trifluoperazine to the enzyme were different from that of haloperidol.