Immunochemical localization of ribulose-1,5-bisphosphate carboxylase in the symbiont-containing gills of Solemya velum (Bivalvia

The distribution of the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase (Rbu P 2 Case; EC 4.1.1.39) was examined by using two immunological methods in tissues of Solemya velum , an Atlantic coast bivalve containing putative chemoautotrophic symbionts. Antibodies elicited by the purified large subunit of Rbu P 2 Case from tobacco ( Nicotiana tabacum ) cross-reacted on immunoblots with a protein of similar molecular mass occurring in extracts of the symbiont-containing gill tissue of S. velum . No cross-reactivity was detected in symbiont-free tissue extracts. The antiserum also cross-reacted in immunoblots with proteins of Thiobacillus neapolitanus , a free-living sulfuroxidizing chemoautotroph whose Rbu P 2 Case has been well characterized. In protein A-gold immunoelectron microscopy studies, this antiserum consistently labeled the symbionts but not surrounding host gill tissue, indicating that the symbionts are responsible for the Rbu P 2 Case activity.