passages.id: split_6_test_705_passage
passages.type: progene_text
passages.text: Immunoprecipitation of AQP4 expressed in Xenopus laevis oocytes demonstrated that heterotetramer formation reflects the relative expression levels of the 32 and 34 kDa polypeptides ; however , tetramers containing different compositions of the two polypeptides exhibit similar water permeabilities .