Collagenase IV is an enzyme purified from Clostridium histolyticum intended for cell and tissue disaggregation of islet tissues/cells (insulin receptor sites). Collagenase is a protease with specificity for the bond between a neutral amino acid (X) and glycine in the sequence Pro-X-Gly-Pro. This sequence is repeated frequently in collagen. Collagenase is unique among proteases in its ability to degrade the triplehelical native collagen fibrils commonly found in connective tissue. The collagenase most commonly used for tissue dissociation is a crude preparation containing clostripiopeptidase A and a number of other proteases, polysaccharidases, and lipases. This crude preparation is ideally suited for tissue dissociation because it contains the enzyme required to attack native collagen and reticular fibres, in addition to the enzymes which hydrolyze the other proteins, polysaccharides, and lipids in the extracellular matrix of connective and epithelial tissues. Crude collagenase can exhibit lot-to-lot variability and may produce occasional toxicity. The activity of these crude collagenase preparations has been correlated with their effectiveness at dissociating specific tissue types leading to the classification of crude collagenase preparations by type.