Identification of an abundant latent 94-kDa gelatin-degrading metalloprotease in human saliva which is activated by acid exposure: implications for a role in digestion of collagenous proteins.

Human saliva was found to contain a latent neutral 94-kDa metalloprotease which degrades denatured collagens. Saliva samples from six normal resting individuals contained an average of 0.34 microgram/ml of latent enzyme. The 94-kDa salivary metalloprotease was found to bind to gelatin and to be immunologically identical to a leukocyte-derived 94-kDa gelatinase/type IV collagenase proenzyme. Exposure of the latent enzyme to acidic conditions (pH 2) followed by neutralization resulted in activation of the proenzyme. The activated enzyme degrades denatured collagens such as gelatin. Since 1-2 liters of saliva is swallowed per day and exposed to gastric acidity, this enzyme could become activated in the gastric compartment and following neutralization in the small bowel, may contribute to the degradation of ingested collagenous proteins.