TUBE GROWTH-PROCESS IN THE DEEP-SEA HYDROTHERMAL VENT TUBEWORM RIFTIA-PACHYPTILA (VESTIMENTIFERA) - SYNTHESIS AND DEGRADATION OF CHITIN

Enzymatic activities involved in chitin metabolism were studied in the giant tubeworm Riftia pachyptila in order to understand the tube grow th process. Experiments performed on repressurized worms provided tiss ues, from the vestimentum and trunk, that were in a secretion state. A nalysis of the composition of the tube newly secreted during these exp eriments showed a chitin content of about 12% and a protein content of about 22%, approximately twofold less than in mature tubes. Chitin sy nthase assays demonstrated the presence of an enzymatic activity funct ioning with UDP-GlcNAc as a substrate. This activity was sensitive to polyoxin D, insensitive to proteolysis by trypsin and stimulated by Gl cNAc. Notable results are the lack of a Mg2+ requirement and stimulati on by chitobiose and chitotriose. The activity, in our experimental co nditions, was shown to be identical in tissues from repressurized anim als and from non repressurized animals rapidly dissected after collect ion. A chitinolytic activity was demonstrated in the opisthosome and i n the plume. These results support the model of tube growth at both en ds (Gaill et al., 1997).