Reaction of tobacco mosaic virus with a thiol-containing imidoester and a possible application to X-ray diffraction analysis

The synthesis of the imidoester methyl 3-mercaptopropionimidate is described; this reacts selectively with the amino groups of proteins. It is intended that the additional thiol groups thereby introduced should serve as points of attachment for heavy atoms and allow the preparation of isomorphous derivatives (at chemically identifiable sites) for X-ray diffraction analysis. Specific reaction of the imidoester with one of the two lysine residues of the protein subunit of intact tobacco mosaic virus is described.     

Pyruvate Kinase of Streptococcus lactis

The kinetic properties of pyruvate kinase (ATP:pyruvate-phosphotransferase, EC 2.7.1.40) from Streptococcus lactis have been investigated. Positive homotropic kinetics were observed with phosphoenolpyruvate and adenosine 5′-diphosphate, resulting in a sigmoid relationship between reaction velocity and substrate concentrations. This relationship was abolished with an excess of the heterotropic effector fructose-1,6-diphosphate, giving a typical Michaelis-Menten relationship. Increasing the concentration of fructose-1,6-diphosphate increased the apparent V_max values and decreased the K_m values for both substrates. Catalysis by pyruvate kinase proceeded optimally at pH 6.9 to 7.5 and was markedly inhibited by inorganic phosphate and sulfate ions. Under certain conditions adenosine 5′-triphosphate also caused inhibition. The K_m values for phosphoenolpyruvate and adenosine 5′-diphosphate in the presence of 2 mM fructose-1,6-diphosphate were 0.17 mM and 1 mM, respectively. The concentration of fructose-1,6-diphosphate giving one-half maximal velocity with 2 mM phosphoenolpyruvate and 5 mM adenosine 5′-diphosphate was 0.07 mM. The intracellular concentrations of these metabolites (0.8 mM phosphoenolpyruvate, 2.4 mM adenosine 5′-diphosphate, and 18 mM fructose-1,6-diphosphate) suggest that the pyruvate kinase in S. lactis approaches maximal activity in exponentially growing cells. The role of pyruvate kinase in the regulation of the glycolytic pathway in lactic streptococci is discussed.     

ADDITIONAL OBSERVATIONS ON STEPHANOSPERMUM OVOIDES,A MIDDLE PENNSYLVANIAN SEED

Taylor , Thomas N. (U. Illinois, Urbana.) Additional observations on Stephanospermum ovoides, a Middle Pennsylvanian seed. Amer. Jour. Bot. 49(7): 794–800. Illus. 1962.—Recently additional specimens of Stephanospermum ovoides have been discovered in coal-ball material collected at the New Delta Mine, Absher, Williamson County, Illinois. Stephanospermum ovoides is a radially symmetrical ovoid seed, characterized by a low sclerotestal crown and micropylar beak. The species stands intermediate in relation to other members in the genus in its sclerotestal elaboration, which is assumed to be reflected in the size of the crown and mieropylar beak.