The binding of the catalytic domain of Thermobifida fusca endoglucanase (EC 18.104.22.168) CDCe15A and exoglucanases (EC 22.214.171.124) CDCe16B and CDCe148A to BMCC was studied. At 5°C, the binding of these CDs to BMCC is rapid with maximum binding occurring just after CD loading. An observed desorption of the bound CDs with time was attributed to the loss of binding sites due to hydrolysis of the easily hydrolysable BMCC. This conclusion was supported by prehydrolysis experiments where the easily hydrolysable BMCC fraction was removed, and binding to the recalcitrant fraction was observed. More of the CDs were bound to the recalcitrant fraction. This was especially true for the exoglucanases, CDCe16B and CDCe148A, where 81-76% of the total CD binding was to the recalcitrant BMCC fraction. The binding to the easily hydrolysable fraction for the endo CDCe15A was 1.5-4 times higher than that of the exo CDCe16B and CDCe148A at the same enzyme concentration. Although CDCe15A saturated the easily hydrolysable fraction of BMCC first, the ratio of the bound to the recalcitrant substrate was constant for CDCe16B and CDCe148A as 81 and 76%, respectively. As the reaction temperature was increased to 50°C, CDCe15A and CDCe148A exhibited a rapid increase in the rate and extent of binding, while CDCe16B exhibited a decrease in the extent of binding.
Bibliographical noteFunding Information:
This research was supported by the United State Department of Agriculture under Agreement No. 98-35504-6176 and the Spencer Family Fund. The authors are grateful to Diana Irwin for her thoughtful scientific comments.
All Science Journal Classification (ASJC) codes
- Applied Microbiology and Biotechnology