Purification and properties of an aspartic protease from potato tuber that is inhibited by a basic chitinase

GUEVARA, M. G.; OLIVA, C.R.; MACHINANDIARENA, M.F.; DALEO, G. R.

PHYSIOLOGIA PLANTARUM

Blackwell Publishing

Año: 1999 vol. 106 p. 164 - 169

0031-9317

A protease was isolated from potato (Solanum tuberosum L. cv. Huinkul) tuber disks after 24 h of aeration, when proteolysis is markedly increased. Purification was performed by ammonium sulfate precipitation, ion exchange chromatography and affinity chromatography. A size of 40 kDa was estimated by SDS-PAGE and gel filtration, it is monomeric and its properties are consistent with those of aspartic proteinases (EC 3.4.23): it had a pH optimum between 4 and 5 and it was inhibited by pepstatin. Partial homology with other plant aspartic proteinases was observed in two sequenced tryptic fragments. It binds to Sepharose-concanavalin A and can be eluted with a-methyl mannoside, indicating that it is possibly glycosylated. Unlike other aspartic proteinases from Solanaceae which degrade pathogenesis-related proteins, it is unable to cleave a basic chitinase from potato. Moreover, this aspartic protease is strongly inhibited by the basic chitinase; the 50% inhibition is obtained when the molar ratio approaches 1, the same as with pepstatin. The interaction between these aspartic protease and a new type of endogenous inhibitor may be an interesting starting point to study the regulation of these aspartic protease during stress.