You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Tryptophan residue at active-site tunnel entrance of Trichoderma reesei cellobiohydrolase Cel7A is important to initiate degradation of crystalline cellulose. Glycoside hydrolase family-7 cellobiohydrolase from Trichoderma reesei (TrCel7A) is one of the best-studied cellulases with the ability to degrade highly crystalline cellulose (HCC). The catalytic domain (cat) and cellulose-binding domain (CBD) are both necessary for full activity on crystalline substrates. Our previous high-speed AFM studies showed that mutation of tryptophan residue (Trp40; W40) at the entrance of the catalytic tunnel drastically decreases the ability to degrade crystalline cellulose. Here, we examined the activities of the wild-type (WT) enzyme and tryptophan to alanine mutant (W40A) enzyme, with and without the CBD, towards various substrates. Evaluation and comparison of the specific activities of the enzymes (WT, WTcat, W40A, and W40Acat) adsorbed on crystalline cellulose indicated that Trp40 is involved in recruiting individual substrate chains into the active site tunnel to initiate processive hydrolysis. This idea was supported by molecular dynamics simulation study, i.e., the reducing-end glucose unit was effectively loaded into the active site of WTcat, but not into that of W40Acat. when the simulation was started from subsite -7. However, when the similar simulations were carried out starting from subsite -5, both enzymes hold the substrate in 50 ns, indicating that the major difference between WTcat and W40Acat is the length of free chain-end of the substrate required to allow initiation of processive movements; this also reflects the difference between crystalline and amorphous celluloses. The CBD is important for enhancing the enzyme population on crystalline substrate, but it also decreases the specific activity of the adsorbed enzyme, possibly by attaching the enzyme to non-optimal places on cellulose surface and/or hindering processive hydrolysis.
{"Chemical": ["glucose", "tryptophan", "alanine", "Trp", "Tryptophan"]}