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

A novel protease has been identified, purified and partially characterised from complete medium grown Spirulina platensis, which could be responsible for the selective proteolysis of phycobiliproteins. It is an 80 kDa homodim eric enzyme; its N-terminal sequence is not related to any known protease s equence. It hydrolyses native phycocyanins in both crude extracts and recon structed systems with purified Allo- or C-phycocyanin. It is inactive on se veral native proteins, including ribulose-1,5-bisphosphate carboxylase. The two phycocyanins are degraded at different velocities since C-phycocyanin is the better substrate, in agreement with the earlier observations on the progress of the phycobilisome disassembly. Specificity for synthetic substr ates and inhibitors strongly suggests its assignment to the serine-protease family. The enzyme, however, is insensitive to the commercially available protein inhibitors of trypsin-like proteases.