Reversal in the kinetics of the M state decay of D96N bacteriorhodopsin: Probing of enzyme catalyzed reactions

The kinetics of M state decay of the D96N bacteriorhodopsin (BR) in the presence of (i) ammonium ion and (ii) an aromatic amine is reported. The M state decay rate becomes faster in the presence of ammonium salt with a concomitant decrease in absorbance maxima at 410 nm. In the presence of an aromatic amine, a slower M state decay rate with an increase in absorbance maxima at 410 nm is observed. The variation in the kinetics of M-state decay is due to the change in the lifetime of the M-state associated with the conversion of M-intermediate to trans-BR. The decay rate of the M-state has also been found to be greatly affected in the presence of enzymatic reactions resulting in the formation of either an acid or a base. Three enzymatic reaction systems, urease, acetylcholinesterase and penicillinase, have been used to study the kinetics of M state decay of D96N bacteriorhodopsin, The kinetic data are found to be dependent on the concentrations of the respective enzyme's substrate. Results of the studies using urea, acetylcholine and penicillin are reported. The enzymes were also immobilized together with D96N bacteriorhodopsin in sol-gel glass to develop a biosensor for the analysis of urea, acetylcholine and penicillin.