This family consists of several phage associated hyaluronidase proteins (EC:184.108.40.206) which seem to be specific to Streptococcus pyogenes and Streptococcus pyogenes bacteriophages. The substrate of hyaluronidase is hyaluronic acid, a sugar polymer composed of alternating N-acetylglucosamine and glucuronic acid residues. Hyaluronic acid is found in the ground substance of human connective tissue and the vitreous of the eye and also is the sole component of the capsule of group A streptococci. The capsule has been shown to be an important virulence factor of this organism by virtue of its ability to resist phagocytosis. Production by S. pyogenes of both a hyaluronic acid capsule and hyaluronidase enzymatic activity capable of destroying the capsule is an interesting, yet-unexplained, phenomenon.