Baillie B K, Yellowlees D
Department of Biochemistry and Molecular Biology, James Cook University, Townsville, Queensland, Australia.
Proc Biol Sci. 1998 Mar 22;265(1395):465-73. doi: 10.1098/rspb.1998.0318.
Carbonic anhydrase (CA) has been purified from the host tissue of Tridacna gigas, a clam that lives in symbiosis with the dinoflagellate alga, Symbiodinium. At least two isoforms of CA were identified in both gill and mantle tissue. The larger (70 kDa) isoform is a glycoprotein with both N- and O-glycans attached and has highest homology to CAII. It is associated with the membrane fraction while the smaller (32 kDa) is present in the aqueous phase in both tissues. The 32 kDa CA has high homology with mammalian CAI at the N-terminus. Both isoforms cross-reacted with antibodies to CAII from chicken. Immunohistology demonstrated that the 70 kDa CA is present within the ciliated branchial filaments and cells lining the tertiary water channels in the gills of T. gigas. This is consistent with a role in the transport of inorganic carbon (Ci) to the haemolymph and therefore supply of Ci to the zooxanthellae. CA was also detected in mantle epithelial cells where it may also contribute to Ci supply to the zooxanthellae. The hyaline body and nerve tissue in the mantle express the 70 kDa CA where it may be involved in light sensing and nervous transmission.
碳酸酐酶（CA）已从巨蛤（Tridacna gigas）的宿主组织中纯化出来，巨蛤是一种与甲藻共生的蛤蜊，这种甲藻为共生藻（Symbiodinium）。在鳃和外套膜组织中至少鉴定出两种CA同工型。较大的（70 kDa）同工型是一种糖蛋白，同时连接有N-聚糖和O-聚糖，与CAII具有最高的同源性。它与膜部分相关，而较小的（32 kDa）同工型存在于两种组织的水相中。32 kDa的CA在N端与哺乳动物的CAI具有高度同源性。两种同工型均与鸡的CAII抗体发生交叉反应。免疫组织学表明，70 kDa的CA存在于巨蛤鳃中纤毛鳃丝和三级水通道内衬细胞内。这与将无机碳（Ci）转运至血淋巴并因此为虫黄藻提供Ci的作用一致。在外套膜上皮细胞中也检测到了CA，它也可能有助于为虫黄藻提供Ci。外套膜中的透明体和神经组织表达70 kDa的CA，它可能参与光感测和神经传递。
