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It has been ascertained that in the Lampetra planeri (Bloch) the muscle and liver aldolase level in the last larval period in which lipids are accumulated strongly increases; this may be due to an increased synthesis or diminished degradation of the enzyme.

The authors suggest a kinetic model with two binding sites for acetylcholinesterase; it is suitable to study particular enzyme forms that show a kinetic pattern which cannot be explained by the model with a single binding site of Krupka and Laidler. The velocity equation was obtained using the algorithm of King and Altman and carrying out elementary calculations.

After having suggested a kinetic model with two binding sites for acetylcholinesterase, the authors obtained the various function of [I] (1/vi; (vo/vi-1)/[I]; 1/Vi; Ki/Vi) starting from the velocity equation. An analytical study was then carried out showing the theoretical shape of such functions at different values of the kinetic parameters.

The authors carried out extraction and purification of an alkaline phosphatase (AP) from Hirudo medicinalis and studied certain characteristics of the enzyme. After homogenizing specimens of H. medicinalis and centrifuging the homogenate at 70,000 g, the enzyme, likely membrane-bound, was obtained in a soluble form by treating the sediment with n-butanol. It was then purified by acetone fractionation and Sephadex G-200 chromatography. A fairly good purification degree was achieved; the enzyme appears to be in a single form and displays a molecular weight of about 268,000. The optimum pH (9.5) is lower than the ones generally observed as regards APs from both Invertebrata and Mammalia. The studied AP displays a strong substrate inhibition, similar to that concerning Metazoa at a higher evolutionary level (Mollusca, Echinodermata). On the contrary, the enzyme-substrate affinity, as shown by Km value (2.447 mM), is lower than as regards APs from more advanced organisms (Echinodermata, Mammalia).