Conidial alkaline phosphatase from Neurospora crassa

Abstract

An alkaline phosphatase was purified from conidia of a Neurospora crassa wild type strain. The Mr of the purified native enzyme was estimated as ca 145000 and 110000 by gel filtration, in the presence and absence of magnesium ions, respectively. A single polypeptide band of Mr 36 000 was detected by SDS-PAGE, suggesting that the native enzyme was a tetramer of apparently identical subunits. Conidial alkaline phosphatase was an acidic protein (pl = 4.0 ± 0.1), with 40% carbohydrate content. Optimal pH was affected by substrate concentration and magnesium ions. Low concentrations of calcium ions (0.1 mM) had slight stimulatory effects, but in excess (5 mM) caused protein aggregates with decreased activity. The enzyme specificity against different substrates was compared with those reported for constitutive or Pi-repressible alkaline phosphatases produced by N. crassa. The results suggested that the conidial alkaline phosphatase represented a different class among other such enzymes synthesized by this organism. Copyright © 1994 Elsevier Science Ltd. All rights reserved.