Question

Site-directed mutagenesis techniques were used to synthesize a mutant citrate synthase enzyme in which the active site histidine was converted to an alanine. Why did the mutant citrate synthase enzyme exhibit decreased catalytic activity?

Answer 1

Ans: In site directed mutagenesio technique, a mutant citrate synthase enzyme ire synthesized by converting the active histidine site with non active alanine site. As a result the catalytic activity of the mutant enzyme decreased. The reason of this activity can be earsity understood from the structure of histidine and alanine. -OH NH OH Histidine miratidine, the imidance midazole part can easily form Alanine In histidine , the imidazoe part in attached with the amino acid residue & and imidazole part contain polar nitrogen atom and one 'NH' group. This part can easily form hydrogen bond with the substrate and increases its catalytic activity. But for alanine one methyl gr. in attached with the amino acid residue and it can not form hydrogen bened with the substrate as it has no lighly electronegative aton As a result the catalytic activity of or group. the entyne her alanine decreases rapidly. Containing are So, the mutant citrate synthase enzyme exhibit decreased catalytic activity due to convertion of active histidine site by non active alanine site: