Transglutaminase expression in rat parotid gland after isoproterenol stimulation

Transglutaminases (E.C. 2.3.2.13) are calcium-dependent enzymes that catalyze the covalent cross-linking of proteins, and occur in multiple molecular forms in a variety of tissues. Distribution of each form of transglutaminase varies with different tissues. Studies were undertaken to characterize the form of transglutaminase expressed in rat parotid gland, and to examine a possible physiological role for the enzyme. It was found that chronic treatment of rats with the beta-adrenergic agonist isoproterenol (IPR) resulted in the induction of parotid transglutaminase activity. The properties of this transglutaminase appeared to be distinct from those of the well-characterized guinea pig liver cytosol transglutaminase (TGase C). The findings that protein polymerization (observed on SDS-PAGE) and incorporation of radioactive putrescine, a polyamine, into protein occur in the presence of exogenous transglutaminase and calcium indicated that certain rat parotid salivary proteins are or could be substrates for this enzyme. Analysis of proteolytic digests of rat parotid salivary proteins on an amino acid analyzer and by high-performance liquid chromatography also indicated that these salivary proteins contain gamma-glutamyl derivatives of primary amines (e.g., polyamines or lysine), post-translational products of transglutaminase catalysis. The possible physiological function of this enzyme in the oral cavity might be stabilization of proteinaceous structures during normal oral homeostasis and/or woundhealing.