Characterization of Pi-repressible enzymes secreted in culture media by Neurospora crassa wild-type cells and null-type mutants

Substrate analysis and molecular cloning of the extracellular alkaline phosphatase of Streptomyces griseus

Streptomyces species secrete large amounts of alkaline phosphatase (AP) enzymes that have not been characterized so far. An AP has been purified to homogeneity from cultures of Streptomyces griseus IMRU 3570. The enzyme has a monomer size of 62 kDa and is processed in the culture to a 33 kDa protein as shown by immunoblotting. The enzyme was purified by ammonium sulfate precipitation, CM-Sephadex cationic exchange, chromatofocusing and HPLC Sphaerogel 3000SW filtration. The pure enzyme uses a variety of organic phosphorylated compounds as substrates. The N-terminal end of the mature protein was found to be RLREDPFTLGVASGDPHP. The gene phoA has been cloned using as probe an oligomer based on the N-terminal sequence of the S. griseus AP. phoA encodes a protein of 62678 Da with low homology to the AP of Escherichia coli. The phoA gene was found to be homologous to three alkaline-phosphatase-encoding genes previously identified in the Streptomyces coelicolor genome. On the basis of the optimal pH, substrate specificity and differences in amino acid sequence of motifs defining the active centre of APs, the S. griseus AP uses a wide range of organic phosphate substrates and is different from the phosphatases of Gram-negative bacteria.

Effects of light on protein secretion in Neurospora crassa

The relative concentrations of secreted proteins in liquid cultures of Neurospora crassa differ in constant darkness compared to constant light (2500 lx). Light reduces the concentrations of some polypeptides markedly and increases the concentrations of protein species of 67, 40, 18 and 13 kDa. The "blind" wc-2 mutant of Neurospora does not show light dependent differences in amounts of secreted proteins. One of the light-sensitive extracellular proteins is shown to be a protease of 17.5 kDa.