Molecular characterisation of a fungal mono(ADP-ribosyl)transferase

A soluble arginine-specific mono(ADP-ribosyl)transferase was detected in dormant spores of Phycomyces blakesleeanus. Soluble proteins incubated with [P-32]NAD revealed, after a two dimensional electrophoretic separation, three major ADP-ribosylated substrates with molecular weights of 38, 37, and 36 kDa and pi values of 6.9, 8.1 and 4.6, respectively. The addition of MgCl2 stimulated the (ADP-ribosyl)transferase activity. This enzymatic activity was stimulated by 250 mu M NO-releasing agent sodium nitroprusside and inhibited with 8 mM benzamide, 0.4 mM meta-IodoBenzylGuanidine (MIBG), and 0.5 mM novobiocin. The three ADP-ribosylation inhibitors affected the germination of Phycomyces spores. The concentrations necessary to inhibit 50% of the spore germination of Phycomyces were 0.05 mM, 0.2 mM, and 8 mM for novobiocin, MIBG, and benzamide, respectively. All the above inhibitors affected the germination process to the same extent, that is, they inhibited the tube protuberation, leaving the spores as swollen cells. These data suggest that ADP-ribosylation may be involved in the germination process of Phycomyces, particularly in germ-tube formation.