ROLE OF SPERMIDINE IN THE ICE-NUCLEATING ACTIVITY OF THE EIM FROM ERWINIA-UREDOVORA KUIN-3

Polyamines have been shown to be necessary for the activity of the ext racellular ice-nucleating matter (EIM) from the ice-nucleating bacteri um, Erwinia uredovora a KUIN-3. When this bacterium was cultured in th e presence of methylglyoxal bis(guanylhydrazone), MGBG (2 mM), the ice -nucleating activity of the EIM significantly decreased. Further, the thermal (25-40 degrees C) and pH (alkaline region) stabilities of the activity were stimulated by the addition of spermidine. This phenomeno n only occurred in the class A and B structures, and it showed that th e hydrophobicities of the class A and B structures in the EIM increase d with the addition of spermidine as judged by the freezing difference spectra. We then found by using fluorescent reagents that the physiol ogical roles of spermidine in the EIM controlled the charge, free-amin o groups, and hydrophobicities on the surface of the EIM. In conclusio n, one could predict that spermidine took part in the charge of the su rface, the control of hydrophobicity, and the stability of protein con formation in the class A and B structures in the EIM, and is a critica l component in the class A and B nucleating structures.