Sptrx-2, a fusion protein composed of one thioredoxin and three tandemly repeated NDP-kinase domains is expressed in human testis germ cells. - Sadek, Christine M.; Damdimopoulos, Anastasios E.; Pelto-Huikko, Markku; Gustafsson, Jan-Åke; Spyrou, Giannis; Miranda-Vizuete, Antonio (Genes to Cells, 2001)