A Limulus glucose-6-phosphatase with phosphotransferase activity characteristic of vertebrate liver microsomes. Its possible evolutionary significance.

1. Limulus hepatopancreas, coxal glands and intestine contain a particulate enzyme which can synthesize glucose 6-phosphate from glucose and inorganic pyrophosphate or carbamyl phosphate as well as hydrolyze glucose 6-phosphate. This has been clearly differentiated from hydrolysis by lysosomal or soluble phosphatases. 2. The enzyme resembles vertebrate glucose-6-phosphatase in its specific anatomical distribution, pH optimum, kinetic properties, donor specificity and phospholipid dependence, as indicated by its satency and lability to detergent treatment. 3. A variety of other invertebrates tested exhibited little or no PPi-glucose phosphotransferase activity with these properties. A similar phosphotransferase activity of lobster hepatopancreas had somewhat different kinetic properties and pH optimum. 4. The hypothesis that a specific glucose-6-phosphatase is to be found only in those animals which utilize free glucose as an important circulating form of energy is presented and discussed. It appears that a variety of transport compounds, such as trehalose and glucose, was tried at the evolutionary level of the Arthropods.