Characterisation of a specific phycocyanin-hydrolysing protease purified from Spirulina platensis

A novel protease has been identified, purified and partiallycharacterised from complete medium grown Spirulina platensis,which could be responsible for the selective proteolysis ofphycobiliproteins. It is an 80 kDa homodimeric enzyme; itsN-terminal sequence is not related to any known proteasesequence. It hydrolyses native phycocyanins in both crudeextracts and reconstructed systems with purified Allo- orC-phycocyanin. It is inactive on several native proteins, includingribulose-1,5-bisphosphate carboxylase. The twophycocyanins are degraded at different velocities since Cphycocyaninis the better substrate, in agreement with theearlier observations on the progress of the phycobilisomedisassembly. Specificity for synthetic substrates and inhibitorsstrongly suggests its assignment to the serine-proteasefamily. The enzyme, however, is insensitive to the commerciallyavailable protein inhibitors of trypsin-like proteases.[...]