TRANSGLUTAMINASE FROM RAT COAGULATING GLAND SECRETION - POSTTRANSLATIONAL MODIFICATIONS AND ACTIVATION BY PHOSPHATIDIC ACIDS

Structural and biochemical characteristics of transglutaminase purifie d by a rapid chromatographic procedure from the rat coagulating gland (anterior prostate) secretion are reported. Fast atom bombardment mapp ing and automated Edman degradation experiments allowed us to verify t hat at least 85% of the entire transglutaminase amino acid sequence is identical to that derived from the cDNA of the major androgen-depende nt rat prostate protein called DP1, The enzyme was found NH2 terminall y blocked and largely posttranslationally modified, since the presence of N-linked oligosaccharides, as well as of complex lipidic structure s, was observed, Mass spectral analysis showed that Asn-408 and -488 a re the glycosylated sites, the N-linked structures identified belongin g to both high-mannose and complex type glycans. The presence of myo-i nositol, of glycerol bound fatty acids, and the high content of mannos e residues, are in agreement with previous observations suggesting, th at a Lipid anchor is bound to coagulating gland secretion transglutami nase, Furthermore, two tightly bound calcium ions per molecule of enzy me were detected, Finally, a strong stimulation of the enzyme activity in vitro by both SDS and a variety of phosphatidic acids was observed . The reported structural and functional peculiarities should definiti vely lead to consider She prostate enzyme as a new member (type IV) of the transglutaminase family.