The chemical evidence for the enzymic activity of lysozyme will be discussed in detail by other speakers at this meeting, but in order to describe our crystallographic studies of the interactions between the enzyme and its substrates it is necessary to summarize briefly what was known about them at the beginning of our work. Simultaneously with his discovery of lysozyme Fleming (1922) discovered a Gram-positive species of bacteria,
Micrococcus lysodeikticus
, which is particularly susceptible to the action of the enzyme. It was not until much later, however, that Salton (1952) demonstrated that the substrate is located entirely within the bacterial cell wall and it is only very recently that its chemical constitution has been established. Valuable early experiments (for example, by Meyer, Palmer, Thomson & Khorazo 1936; Meyer, Hahnel & Steinberg 1946; and by Epstein & Chain 1940) showed that lysozyme releases
N
-acetyl-amino sugars from
M. lysodeikticus
, but the first indication of the type of linkage attacked by lysozyme came when Berger & Weiser (1957) showed that lysozyme also degrades chitin, the linear polymer of
N
-acetylghicosamine.
