The microbial degradation of cellulose and xylans requires several types of enzymes such as endoglucanases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91) (exoglucanases), or xylanases (EC 3.2.1.8) [1,2]. Fungi and bacteria produces a spectrum of cellulolytic enzymes (cellulases) and xylanases which, on the basis of sequence similarities, can be classified into families. One of these families is known as the cellulase family B [3] or as the glycosyl hydrolases family 6 [4,E1]. The enzymes which are currently known to belong to this family are listed below.

• Agaricus bisporus exoglucanase 3 (cel3).
• Cellulomonas fimi endoglucanase A (cenA).
• Cellulomonas fimi exoglucanase A (cbhA).
• Microspora bispora endoglucanase A (celA).
• Streptomyces halstedii endoglucanases A (celA1).
• Streptomyces strain KSM-9 endoglucanase 1 (casA).
• Thermomonospora fusca endoglucanase E-2 (celB).
• Trichoderma reesei exoglucanase II (CBH2).

One of the conserved regions in these enzymes contains a conserved aspartic acid residue which is potentially involved [5] in the catalytic mechanism; the aspartate is followed by a cysteine which is involved in a disulfide bond [6]. A second conserved region contains an aspartate which seems [5] to be the proton donor in the catalytic mechanism. We have used both regions as signature patterns.