A monomeric acidic protein of 14 000 Da with an isoelectric point of 4.5 was isolated from Mycobacterium phlei, which stained poorly with Coomassie brilliant blue. This protein showed retardation in mobility in SDS-PAGE upon treatment with calcium, similar to eukaryotic calmodulin proteins. Activation of cAMP phosphodiesterase and NAD kinase by this protein was observed. The CD spectral analysis indicated that the CALP has 52% of L-conformation. The regular L-conformation of the calmodulin like protein was shifted to 46% K-helical structure when calcium ions reacted with the protein, however, 42% of the CALP still retained its original L-conformation. These observations indicated homology of this calcium binding protein with that of eukaryotic calmodulins in few structural and functional properties. z 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.