Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.59 (MIP)
 4,906 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A new member of water channels has been identified from rat testis. This gene, termed aquaporin 8 (AQP8), encoded a 263-amino-acid protein that contained the conserved NPA motifs of MIP family proteins. AQP8 has amino acid sequence identity with other aquaporins (approximately 35%) and highest with a plant water channel, AQP-gamma TIP (39%), suggesting that AQP8 is a unique member in mammalian aquaporins. The expression of AQP8 in Xenopus oocytes stimulated the osmotic water permeability (Pr) 8.5 folds. The increase of Pr was inhibited with 0.3 mM mercury chloride by 55%, which was reversed with mercaptoethanol. The Arrhenius activation energy for the stimulated water permeability was low (5.1 kcal/mol). AQP8 did not facilitate glycerol transport. Northern blot analysis revealed a 1.5-kb transcript of AQP8 abundantly in testis and slightly in liver. In situ hybridization of testis revealed the expression of AQP8 mRNA in all stages of spermatogenesis from primary spermatocytes to spermatids in seminiferous tubules. Together with previously cloned AQP7, AQP8 may also play an important role in spermatogenesis. The unexpected complexity of the presence of two aquaporins in testis may call for the further analysis of the role of aquaporins in the reproduction biology.
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PMID:Cloning and functional expression of a second new aquaporin abundantly expressed in testis. 929 32

An aquaporin-type water channel was isolated from mouse based on homology to known aquaporins. A 1447 bp cDNA was sequenced (designated AQP8) with a 783 bp open reading frame encoding a 261 amino acid hydrophobic protein which contained the conserved NPA motifs of MIP family members. Amino acid alignment showed greatest homology of AQP8 to plant water channel gamma TIP (38% identity) followed by mammalian water channels AQP4 (32%) and AQP2 (31%). Northern blot analysis indicated a 1.7 kb transcript expressed strongly in placenta > colon > liver approximately heart. RT-PCR with AQP8-specific primers and Southern blot analysis showed AQP8 transcript in the above tissues and in pancreas, lung, kidney, submandibular gland, diaphragm, testis, spleen, stomach and brain. Expression of AQP8 cRNA in Xenopus oocytes increased osmotic water permeability from (0.8 +/- 0.1) x 10(-3) cm/s to (22 +/- 3) x 10(-3) cm/s (10 degrees C) in a mercurial-sensitive manner. AQP8 was also permeable to urea but not to glycerol. Normalization for oocyte plasma membrane expression using cMyc-tagged AQP8 indicated a single channel water permeability of 8.2 x 10(-14) cm3/s. AQP8 is unique among the water channels in terms of its urea permeability and its strong expression in gastrointestinal organs, placenta and heart.
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PMID:Cloning of a novel water and urea-permeable aquaporin from mouse expressed strongly in colon, placenta, liver, and heart. 938 76