Adenylate Cyclase Activity in Neurospora crassa

Adenylate cyclase, the enzyme responsible for cyclic adenylate synthesis has been found in membrane fractions of animal cells (l-4). This enzyme system is stimulated by several hormones, showing a wide range of specificity. The occurrence of a similar enzyme activity has been also demonstrated in Escherichia coli and Bacillus liquejaciens (5-7)) but in these organisms the mechanism that regulates cyclic adenosine 3’, 5’-monophosphate synthesis is poorly understood. Recent pieces of evidence indicate that in Neurospora crassa some of the mechanisms designed for the amplification of environmental signals seem to be well evolved. In fact, glycogen metabolism in this ascomycete fungus resembles that of animal cells (8, 9). Glycogen synthetase (UDP-glucose :glycogen cy1,4-glucosyltransferase, EC 2.4.1.11) and phosphorylase ((Y1,4-glucan : orthophosphate glucosyltransferase, EC 2.4.1.1) have two interconvertible forms, and as it also occurs in mammalian tissues, conditions for the activation of one of these enzymes appear to be roughly similar to those required for the inactivation of the other and vice versa. Moreover, conversion of the inactive to the active form of glycogen phosphorylase in mycelial extracts proceeds at a higher rate in the presence of cyclic adenosine 3’) 5’-monophosphate. The purpose of this paper is to report evidence indicating that membrane preparations from N. crassa catalyze the synthesis of cyclic AMP.’ The companion paper presents an account of some properties of this enzymatic system.