Steady-state fluorescence anisotropy changes of 1,6-diphenyl-1,3,5,-hexatriene in membranes from Bacillus megaterium spores

The steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene incorporated into isolated Bacillus megaterium spore membranes was measured. Compounds capable of triggering spore germination in vivo caused an increase in the anisotropy of diphenylhexatriene. These increases in anisotropy of diphenylhexatriene in spore membranes are likely to represent at least a portion of the trigger mechanism for spore germination based on the following observations. First, there was an exceptional positive correlation between compounds that both triggered germination in vivo and caused changes in anisotropy in vitro. Second. the capacity of membranes to respond to germinants by increases in anisotropy was unique to membranes from spores but disappeared after germination. Third, alteration of spores chemically or genetically to block the in vivo triggering of germination by l-proline also blocked the in vitro anisotropy change with l-proline but not d-glucose. Finally, there was no correlation between the transport activities of specific compounds and the ability of these compounds to either trigger germination or alter the anisotropy of diphenylhexatriene in the membranes. Although we do not known the nature of the molecular interactions giving rise to the anisotropy changes, we hypothesize that they are due to changes in protein conformation that alter protein-protein and/or protein-lipid interactions. Such modifications of membrane structures could account for the rapid release of small molecular weight compounds such as K⁺ and Ca²⁺ early in germination.