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Germination-initiating Activities for Bacillus subtilis Spores of Analogues of l-Alanine Derived by Modification at the Amino or Carboxyl Group
Abstract
The ability of 13 amino-group-modified and 12 carboxyl-group-modified l-alanine derivatives to initiate germination of Bacillus subtilis spores was examined. The ‘relative affinity’, defined as the ratio of the concentration of l-alanine required to give 20% of the maximal germination rate to the concentration of analogue required to give this same rate, was used to estimate the effectiveness of the analogues as germinants. l-Ala-l-Ala had a relative affinity of only 1/4200. For most of the l-alanyl dipeptides studied (with the exception of l-Ala-l-Pro and l-Pro-l-Ala), their effectiveness as germinants was lower if the second amino acid was substituted in the carboxyl group rather than the amino group of l-alanine. N-(2-Methylsulphonyl)ethyloxy-carbonyl-l-Ala was a good germinant (relative affinity 1/100), indicating that there may be an additional complementary site for this group in the germinant receptor field on the spore. Compounds with a shorter chain, N-t-butoxycarbonyl-l-Ala and N-acetyl-l-Ala, showed lower affinities, and compounds with an aromatic ring were very poor germinants. Replacement of the carboxyl group of l-alanine by an alcohol group caused a total loss of germinant activity, and its modification by conversion to an amide group or by substitution of amino acids resulted in low affinity and germination rates. Esterified l-alanine derivatives retained high activity, suggesting that retaining an electronegative group was important. The stimulatory effect of glucose on germination was very marked for compounds with a hydrophobic substituent in either the amino or the carboxyl group, such as l-Leu-l-Ala, l-Ala-l-Leu, N-carbobenzoxy-l-Ala and N-dinitrophenyl-l-Ala. Overall, it can be deduced that both -NH- and -COO- groups, separated by 1 or 2 interatomic distances, are important for germinant activity. Substituents in the amino group were tolerated better than those in the carboxyl group.
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© Society for General Microbiology 1988