Limited hydrolysis of levan by a levanpolyase system

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Abstract
Enzyme systems which effect the hydrolysis of a bacterial levan were adaptively formed by a range of soil micro-organisms. There were at least three distinct enzyme types in this group: (a) A system ("levanpolyase") which converted levan into end products consisting of two homologous polymer series (1-R-and 6-R-fructose) ranging continuously in n from 2 to at least 12, with a maximum in the range 9 [plus or minus] 2. (b) A system which converted levan into end products all of which had n> 8. (c) A system whose action on levan gave only levanbiose and a high-molecular-weight product. Exhaustive action of the levanpolyase system on levan gave 1-R- and 6-R-fructose in equimolar amounts that were the equivalent of the branching degree of levan as estimated by methylation analysis. It can thus be inferred that susceptible linkages in levan were all of the type 2[forward arrow]6, and that one -half of these were at C -2 of fructose units which have a substituent on C-1. Sucrose and raffinose were not cleaved by this system, whereas inulin was hydrolysed to an extent of only 3.0% and gave end products which all had n>5. Whereas typical preparations of levanpolyase formed no free fructose from levan, inulin or sucrose, cells grown on levan after frequent prior transfers on nutrient agar gave an enzyme system which did hydrolyse sucrose, hydrolysed inulin totally and afforded both fructose and a twin-polymer series (1-R- and 6-R-fructose) among the end products formed from levan. A hypothesis is proposed which may account for the observed differential activity of levanpolyase on apparently similar linkages within the structure of a levan.