Chitin, a (1-4)-linked polymer of 2-acetamido-2-deoxy-(3-o-glucose, is a major structural component of the exoskeleton of invertebrates and the cell wall of fungi' . The polysaccharide chain can be folded either in an antiparallel or parallel conformation to form a-or Q-chitin, respectively . The a-form is the more stable and common conformation in Nature .
Chitin chains are usually found as a lattice of highly crystalline microfibrils within an amorphous polysaccharide or protein matrix . These microfibrils can be observed readily by extracting the embedding matrix by enzymic or chemical hydrolysis, shadow casting the chitinous residue with a heavy metal, and examining the material in the electron microscopez-5 . Studies of fungal chitins have shown that the microfibrils can vary in length and width4'6'7 . Also, those fungi that grow by a process of budding and cell division have short fibrillar crystals of chitin which appear to fit together like a mosaic, whereas filamentous branching fungi have long microfibrils that are tightly woven into a three-dimensional network7 . Therefore, the shorter crystal of chitin may meet the biophysical requirements of walls of spherical cells, whereas the longer fibrils may better suit tubular structures such as fungal hyphae .
The J3-chitin molecule can also be used to form structures with differing properties . For instance, the long chitinous spines of some marine diatoms (for example, Thalassiosira fluviatilis) are stiff, whereas the j3-chitin in the cephalopod pen allows greater flexibility and plasticity .
We now report on the spectroscopic properties of a range of a-and /3-chitin .
Chitin, chemically extracted from Candida albicans, bound fluorescently