Enzymatic depolymerization of abundant polysaccharides such as chitin and cellulose is hampered by the recalcitrant, crystalline nature of these materials. Nature musters a large variety of hydrolytic and oxidative enzymes with varying properties that, together, manage the task of saccharifying chitin and cellulose. Processivity, i.e. the ability to carry out multiple hydrolytic reactions while sliding along the polysaccharide chain, is considered a key property of hydrolytic enzymes acting on the most recalcitrant parts of the substrate. Due to the insoluble nature of the substrate, this phenomenon is difficult to study. For family GH18 chitinases, the combination of a catalytic mechanism depending on acetyl groups in the substrate and the possibility to produce partially deacetylated soluble single chitin chains (chitosan) provides a unique tool for studying processivity. Here, we review how the use of well-defined chitosans has helped unraveling crucial and otherwise difficult to study properties of multiple chitinases, including well studied chitinases from Serratia marcescens and human chitotriosidase (HCHT). These studies have yielded pioneering insights into the structural basis and functional implications of processivity that apply to both chitinases and cellulases. Recent studies of processive chitinases and cellulases confirm the insights originally derived from the work with chitosan and take this further, for example by providing kinetic and thermodynamic data for processive enzyme action.

这些材料的顽强结晶性阻碍了丰富的多糖（例如几丁质和纤维素）的酶解聚。大自然聚集了多种具有不同性质的水解和氧化酶，这些酶共同控制糖化几丁质和纤维素的任务。加工性，即沿着多糖链滑动时进行多种水解反应的能力，被认为是水解酶作用于底物最难降解部分的关键特性。由于底物的不溶性，这种现象很难研究。对于家庭GH18几丁质酶，取决于底物中乙酰基的催化机制与产生部分脱乙酰基的可溶性几丁质单链（壳聚糖）的可能性的结合，为研究可加工性提供了独特的工具。在这里，我们回顾使用定义明确的壳聚糖如何帮助弄清关键的，否则难以研究的多种几丁质酶的特性，包括来自粘质沙雷氏菌和人类壳三糖苷酶（HCHT）。这些研究已经产生了对适用于几丁质酶和纤维素酶的持续性的结构基础和功能含义的开创性见解。进行性几丁质酶和纤维素酶的最新研究证实了最初从壳聚糖的研究中获得的见解，并通过例如提供用于进行性酶作用的动力学和热力学数据来进一步推广。