A 90-kDa protein-actin stable complex was purified from blood platelets by a short and efficient procedure giving at the same time actin used in polymerization assays. 90-kDa protein free of actin was prepared from the complex by 8 M ureau treatment and renaturation. By its molecular mass, immunological cross-reactivity with macrophage gelsolin and its effect on G- and F-actin the 90-kDa protein appears as the platelet gelsolin.

Two forms, A and B, of octopine dehydrogenase from Pecten muximus L. straited adductor muscles were separated by ion-exchange chromatography and purified to homogeneity. Their kinetic properties were similar and, among others, the mnemonical behaviour, previously found for octopine dehydrogenase, was confirmed. Structural features, determined by polyacrylamide gel electrophoresis with and without sodium dodecylsulfate, amino acid composition, immunological tests and heat stability were compared. The only differences between the two forms are their charge and their sensibility to various chemical treatments. Assays of reciprocal conversion of the two forms by oxidation, reduction or deamidation failed. No tissue specificity and no relation to any physiological conditions could be observed. However, a constant ratio A:B = 1:4 was statistically found in crude extracts as well as in the purified enzyme. It therefore seems possible to assume that the two forms of octopine dehydrogenase pre-exist in living P. maximus, although their genetic origin has to be established.

The amino acid composition of octopine dehydrogenase from muscles of Pecten maximus was determined. The calculate dpartial specific volume of 0.74 allowed us to evaluate the molecular weight of the enzyme as 38000. It is concluded that this enzyme consists of a single polypeptide chain on the basis of the molecular weight determined from equilibrium ultracentrifugation in 6 M guanidine hydrochloride and from electrophoresis on polyacrylamide gel containing sodium dodecylsulfate as well as on the basis of the number of peptides obtained by tryptic digestion. The presence of one essential –SH group per mole of enzyme and of one binding site for NADH are also consistent with the existence of a single active center. No NH 2 ‐terminal amino acid can be detected by reaction with dansyl chloride and with phenyl‐isothiocyanate.