A putative proline iminopeptidase of Thermotoga maritima is a leucine aminopeptidese with lysine-p-nitroanilide hydrolyzing activity

作者：Ratnayake S; Selvarkumar P; Hayashi K^*

来源：Enzyme and Microbial Technology, 2003, 32(3-4): 414-421.

DOI：10.1016/S0141-0229(02)00311-3

• leucine aminopeptidase
• Thermotoga maritima
• cloning
• thermostability
• substrate specificity

A putative aminopeptidase P gene (TM0042, Swissport Q9WXP9, GeneBank AAD35136) of Thermotoga maritima was cloned and expressed in Escherichia coli BL21 (RIL). The enzyme was purified by the combination of ion exchange chromatography; Q-Sepharose and Mono-Q column. The purified recombinant T maritima aminopeptidase P enzyme, gave a homogenous protein band with an apparent molecular weight of 40 kDa in SDS-PAGE analysis. The enzyme was purified 23-fold with the specific activity of 16.5 unit/mg with the final recovery of 22%. The enzyme was thermostable up to 90 degreesC for 30 min. An optimal activity was observed at 90 degreesC at pH 7.5. The purified enzyme was stable between pH 6.5 and 8 at 80 degreesC with the optimum of pH 7.5. Based on the amino acid sequence, the enzyme belongs to M 24B family of metalloenzymes. None of the divalent cations enhance the activity of the enzyme while Pb2+, Cu2+, Co2+, Cd2+, and Zn2+ were inhibitory to the enzyme activity. Divalent cation of Mg2+ showed 100% enzyme activity, to a lesser extent, Ca2+ and Mn2+ whereas strong inhibition of enzyme activity was observed with Zn2+ and Cd2+. The enzyme designated as putative aminopeptidase P was very low activity in hydrolyzing proline-p-nitroanilide. Kinetic studies on the purified enzyme confirmed that the enzyme is a leucine aminopeptidase. Enzyme also hydrolyzes lysine-p-nitroanilide with efficiency comparable to that of leucine-p-nitroanilide. This is the first report of leucine aminopeptidase with lysine-p-nitroanilide hydrolyzing activity, which belongs to the M 24B family of metalloenzymes.

• 出版日期2003-3-3