Manometric studies of bracken [Pteridium aquilinum (L.) Kuhn] thiaminase

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Abstract
The transfer reaction of bracken thiaminase can lead to the production of H+ ions. Under these conditions the reaction can be studied manometrically in bicarbonate-carbon dioxide buffer. When aniline, piperidine, pyridine and trimethylamine are used as acceptor amines with thiamine in limiting amount, about 5-10% of the thiamine may be lost in side reactions but there is a reasonable agreement between the calculated and experimental CO2 output. The effect on the rate of bracken thiaminase action of varying the concentration of thiamine and the concentration and type of acceptor amine were studied. The manometric method was used to demonstrate that heteropyrithiamine, quinilino-thiamine and possibly oxythiamine are thiaminase substrates. The effect of several structural analogs of thiamine on bracken thiaminase was studied; 3-(o-aminobenzyl)-4-methyl-thiazolium chloride is a powerful but noncompetitive inhibitor. Conditions are described under which the rate of evolution of CO2 is directly proportional to the amount of bracken-thiaminase preparation present. It is suggested that the manometric method could be used for estimating thiaminase activity.