(1) Three parental fructose diphosphate aldolases, A, B, and C, were detected in tissues of each of 13 vertebrate species tested (including man). The following criteria of identification were employed: relative electrophoretic mobilities to the well-studied rabbit and rat prototype enzymes; substrate specificities (fructose diphosphate/fructose 1-phosphate activity ratio); tissue distributions, and, in some cases, specific immunological properties. A fourth parental aldolase form was detected in trout and salmon but not in other fish studied. (2) In vertebrate tissues containing two of the parental aldolases, five-membered hybrid sets were usually detected, indicating that both aldolases were formed in individual cells. Five-membered hybrid sets were detected in some tissues of all species examined. This suggests that the parental aldolases in vertebrates are tetrameric molecules. (3) Aldolases A, B, and C have a segregated tissue distribution. Aldolase A was present in most tissues investigated; aldolase B was detected in liver and kidney; aldolase C was found in brain and somewhat more variably in heart, spleen, and other tissues. (4) Transitions from a predominance of aldolase A to B in liver and kidney and A to C in brain have been observed in man. C to A transitions were observed in chicken muscle and heart, and in human heart. These transitions emphasize the independent regulation of synthesis of the three aldolases. (5) No evidence of multiple tissue-specific aldolases corresponding to those of the vertebrates was found in invertebrates or plants, although aldolase multiplicity was detected in some species. It is proposed, therefore, that the homologous aldolase genes B and C were functionally consolidated in the vertebrates. (6) Single bands of class II aldolase activity were found in all bacteria and fungi tested. In confirmation of previous work, a single class I and a single class II activity was detected in Euglena. (7) The aldolase from Micrococcus aerogenes was not inhibited by chelating agents, suggesting this enzyme may be a class I aldolase. No class I aldolases have been found previously in microbial systems. © 1969, American Chemical Society. All rights reserved.
