The nucleotide sequence of clone pTT26 (3786 bp), containing the gene for 1,3-β-glucanase LamA (laminarinase) from was determined. It contains an ORF encoding a protein of 646 aa (73 328 Da). The central part of the protein is homologous to the complete catalytic domain of bacterial and some eukaryotic endo-1,3-β--glucanases and belongs to family 16 of glycosyl hydrolases. This domain is flanked on both sides by one copy on each side of a substrate binding domain homologue (family II). The recombinant laminarinase protein was purified from host cells in two forms, a 73 kDa and a processed 52 kDa protein, both having high specific activity towards laminarin (3100 and 2600 U mg, respectively) and values of 2.8 and 2.2 mg ml, respectively. Limited activity on 1,3-1,4-β-glucan (lichenan) was detected (90 U mg). Laminarin was degraded in an endoglucanase modus, yielding glucose, laminaribiose and -triose as end products. Thus LamA classifies as an endo-1,3(4)-β-glucanase (EC The optimum temperature of the enzymes was 95 ° (73 kDa) and 85 ° (52 kDa) at an optimum pH of 6.2. The superior thermostability of the 73 kDa enzyme is demonstrated by incubation without substrate at 100 °, where 57% of the initial activity remained after 30 min (82% at 95°). Thus, LamA is the most thermostable 1,3-β-glucanase described to date.


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