Light- and electron-microscopic histochemical procedures were used to show the distribution of the membrane-bound enzymes alkaline phosphatase (Alp), adenosine triphosphatase (ATPase), and 5′-nucleotidase (5′-nuc) in the livers of lamprey,Petromyzon marinus, throughout the life cycle. In larvae, the three enzymes are located at the biliary pole on the canalicular membranes of microvilli. At metamorphosis the enzymes become localized at all lateral cell surfaces of hepatocytes as bile canaliculi degenerate in the programmed regression of the entire biliary tree. This latter pattern of enzyme distribution persists during the parasitic adult phase but no activity is evident in individuals in the spawning migration. As the timing of the relocalization of enzymatic activity correlates well with a build-up of bile products and iron during metamorphosis, it is suggested that the lateral surface may be the new site for transport of these produ
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