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We have cocrystallized the drug ethidium bromide with the dinucleoside monophosphate 5-iodouridylyl(3'-5')adenosine and have solved the three-dimensional structure to atomic resolution by x-ray crystallography. This has allowed the direct visualization of intercalative binding by this drug to a fragment of a nucleic acid double helix.

The stress concentrations due to an elliptical cutout in a shallow cylindrical shell are determined by means of a system of singular integral equations, solved numerically. Three loading conditions are considered: tension, torsion, and internal pressure. Results confirm those obtained by previous authors by other methods and extend the range of parameters over which results are available.

The transient thermocouple response characteristics in deflagrating low-conductivity materials with high temperature gradients were investigated theoretically and experimentally. The theoretical model considers the thermocouple bead and lead wires separately, and the two resulting partial differential equations are solved simultaneously by a finite difference technique. The experimental results are obtained by embedding various size thermocouple wires in double-base solid propellants and consequently measuring the temperature profiles and the surface temperatures. The theoretical model is used to predict the experimentally measured temperatures. There is good agreement. The experimentally measured values are smaller than the correct surface temperature, corresponding to the model prediction for zero wire diameter, by at least 20 percent even when 1/2-mil thermocouple wire is used. Both the experimental and theoretical results show a plateau when the thermocouple bead emerges from the solid into the gas phase. The theoretical results also show that there is an optimum ratio of. the thermocouple bead diameter to the wire diameter, which is found to be close to three

The ‘malic’ enzyme (EC 1.1.1.40) has been purified (300-fold) from wheat germ and its abilities to catalyse the decarboxylation and the hydrogenation of oxaloacetic acid and oxaloacetate esters was studied. The free 1-carboxyl group is essential for the interaction of oxaloacetates and substituted oxaloacetates with the enzyme via cations. The free 4-carboxyl group is required for the decarboxylation but is not indispensable for the hydrogenation. At high concentrations, cations inhibit the enzymic hydrogenation of oxaloacetic acid but not that of 4-ethyl oxaloacetate. A plausible inhibitory mechanism is proposed.

Measurements are reported on the kinetics of the lysozyme-catalysed hydrolysis of several β-aryl di-N-acetylchitobiosides, some of which have been synthesized for the first time. The catalytic rate constants (kcat.) at 45° yield a curved Hammett plot (concave up) and the plot of ΔH‡ versus ΔS‡ has a sharp break. Substrates with electron-withdrawing groups exhibit a kinetic deuterium isotope effect (kHcat./kDcat.), whereas those with electron-donating groups show no such isotope effect. The results suggest the operation of different mechanisms for the two types of substrates.

The mammalian pyruvate dehydrogenase complex contains a core, consisting of dihydrolipoyl transacetylase, to which pyruvate dehydrogenase and dihydrolipoyl dehydrogenase (a flavoprotein) are joined. The lipoyl moiety is bound covalently to the transacetylase and, presumably, rotates between the catalytic centers of the three different enzymes that comprise the complex.

Maize (Zea maysL.) endosperms from normal, brittle‐2, and shrunken‐2near‐isogenic sublines of the Oh43 inbred were assayed for nucleoside diphosphate glucose pyrophosphorylase activity at 10, 20, and 30 days post‐pollination. Polyethaleneamine‐cellulose thin layer chromatography and polyacrylamide gel electrophoresis were used for product assay and identification of isoenzyme patterns from crude enzyme preparations, respectively. Evidence is presented for the existence in corn endosperm of pyrophosphorylose activity with guanosine triphosphate and thymidine triphosphate in addition to adenosine triphosphate, cytidine triphosphate, and uridine triphosphate. Two adenosine diphosphate glucosepyrophosphorylase isoenzyme bands from normaland shrunken‐2endosperms were detected with the same pattern, suggesting that the shrunken‐2 gene may be regulatory in nature. Brittle‐2showed an altered mobility of the adenosine diphosphate glucose pyrophosphorylase banding pattern, which indicates that brittle‐2may be a structural gene. Three isoenzymes for uridine diphosphate glucose pyrophosphorylase were found in normal and mutant endosperms. Evidence indicated that guanosine triphosphate may be utilized by adenosine diphosphate glucose pyrophosphorylase. Thymidine triphosphate and possibly cytidine triphosphate may be utilized by uridine diphosphate glucose pyrophosphorylase. There were no differential appearances of the pyrophosphorylase isoenzymes during corn endosperm development. However, quantitative differences in the isoenzyme bands were observed.