Structure of the actin-myosin interface

The topography of the rigor complex between F-actin and myosin heads (S1) has been investigated by carbodiimide zero-length cross-linking. The results demonstrate for the first time that the 95,000-molecular weight (95K) heavy chain of the myosin head enters into van der Waals contact with two neighbouring actin monomers; one is bound to the 50K domain and the other to the 20K domain of the myosin chain. The covalent F-actin-S1 complex can be isolated; it shows a vastly elevated Mg2+-ATPase. Each pair of actin subunits in the thin filament seems to act as a functional unit for specific binding of a myosin head and stimulation of its Mg2+-ATPase activity.     

Nitrogen fixation in deteriorating wood

Résumé Divers types de bois ont été détériorés par des microorganismes du sol et leur capacité de réduction de l'acétylène mesurée. L'éthylène produit a révélé l'existence d'une activité nitrogénasique et suggéré que des microorganismes fixateurs d'azote peuvent pénétrer et vivre dans le bois.

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Acknowledgment. The authors wish to record their gratitude to Dr.J. F. Levy for his encouragement in this study and one author (R. F. S.), is grateful to the Department of the Environment for financial assistance.