Bioluminescence of photobacterium fischeri

Abstract

The bioluminescence of the bacterial system was considered to be consist of two separated steps. One is the activation of the molecular oxygen by the cofactor of the enzyme, reduced FMN, to form complex-I in which the cofactor is known to be the form of 4a-hydroperoxy FMN, and the other is the oxidation of the substrate, aliphatic aldehyde of longer chain than heptyl aldehyde, to the corresponding carboxylic acid. The complex-I is relatively stable, and can be isolated in pure form by low temperature chromatographic methods. The reaction between the isolated complex-I and long chain aliphatic aldehyde can be executed in one step reaction, in which the chemiexcitation to generate an electronically excited state and to emit bioluminescence was included. The specificity of alkyl chain of aldehyde was examined, and for the first time the acetaldehyde was found to be a substrate of the complex-I producing weak luminescence and acetic acid at relatively high concentration (Km = 7-8 mM), while other short chain aldehydes from propyl aldehyde to hexyl aldehyde were found not to be efficient substrates. The acetaldehyde-induced bioluminescence was greatly stimulated to that of regular long chain aldehyde reaction by addition of long chain alkyl compounds, aldehydes or not, and the degree of stimulation is dependent upon the chain length and the polar head group of included alkyl compounds, which are competetive inhibitors of long chain aldehydes in regular reaction. n-Octyl bromide is found to be most efficient stimulant, and the chain length of nonyl or decyl group is optimal. The production of acetic acid was also increased by long chain alkyl compounds, suggesting the specificity of chain length of aldehyde and changed reactivity of complex-I to the included formal group, either of acetaldehyde or long chain aldehyde. The binding constants of long chain alkyl compounds to the complex-I to form complex-I`` were in the range of $10^5-10^7$M, which were dependent upon t...