A Direct Synthesis of Unsaturated Uracil Nucleosides from Silylated Uracil and Triacetylglucal

A kinetic analysis of splitting oligomeric substrates by poly(β-D-mannuronate)lyases (alginate lyases I, SP1 and SP2) from a marine mollusk was done. Monomer and oligomers of mannuronate and guluronate were prepared by hydrolyzing poly β-1,4-D-mannuronate and poly α-1,4-L-guluronate from alginate with H₂SO₄, respectively, and thereafter by gel filtration on a Bio-Gel P-2 column. Alginate lyases I apparently did not act on the trimer of mannuronate but did on the tetramer or those longer than that, indicating the increased k_cad/K_m with increasing polymerization degree. The kinetic analyses suggest that the size of the subsite structure of the enzymes is most likely to be able to bind the linear pentamer of mannuronate units.