Properties of Repressible Alkaline Phosphatase from Wild Type and a Wall-less Mutant of Neurospora crassa”

The repressible alkaline phosphatase of Neurospora crassu was purified from both the mycelium of a wild type strain and from the medium in which cultures of the slime mutant (which lacks the normal cell wall) had been grown. The enzyme preparations from the two sources had similar amino acid compositions, immunological properties, specific activities, thermal stabilities, and kinetic constants, but differed in a number of other properties. Both enzyme preparations contained carbohydrate, but the carbohydrate content of the enzyme isolated from slime medium was almost double that of the enzyme from wild type mycelium (24 and 14 %, respectively). The molecular weight of the enzyme secreted by slime cells, estimated by gel filtration on Sephadex G-200 and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, was higher than that of the enzyme from wild type mycelium by an amount consistent with its increased carbohydrate content. Electrophoresis at pH 4.7 and 9.5 indicated that the enzyme isolated from slime medium is more anionic than the enzyme from wild type mycelium. Chemical analysis revealed the presence of approximately 8 phosphate groups per enzyme molecule in the purified slime extracellular enzyme, whereas the wild type enzyme contained less than 0.5 phosphate molecule per enzyme molecule. The presence of phosphate in the slime extracellular enzyme, and the lack of significant amounts of phosphate in the wild type mycelial enzyme, was also demonstrated by determination of a2P associated with the enzymes isolated from the two sources following derepression in the presence of 82P04a-. A significant portion of the repressible alkaline phosphatase produced by derepressed wild type N. crassa was found to be secreted into the growth medium. The electrophoretic mobility of the enzyme isolated from the wild type culture medium resembled that of the enzyme isolated from the slime culture medium rather than that of the enzyme isolated from wild type mycelium.