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The effects of norharman, one of the few known inhibitors of the heme protein indoleamine 2,3-dioxygenase, and of 4-phenylimidazole (4-PheImid), a heme ligand, on the catalytic (Vmax, Km) and spectroscopic properties (optical absorption, CD, and magnetic CD) of the rabbit small intestinal dioxygenase were investigated. Assays were performed with the substrate L- or D-tryptophan (Trp) and an ascorbic acid-methylene blue cofactor system at 25 degrees C. This study has revealed that both norharman and 4-PheImid exhibit noncompetitive inhibition with respect to L-Trp and D-Trp. The binding of norharman to the enzyme results in the formation of a low-spin complex in both the ferric and ferrous enzyme with comparable dissociation constants (Kd = approximately 10 microM at pH 7.0) that are about 10 times smaller than the observed Ki value. L-Trp exerts no effect for the ferric enzyme and slight negative cooperative effects for the ferrous enzyme on norharman binding. Close spectral similarities are observed between the adducts of the enzyme with norharman and 4-PheImid in the respective oxidation states. This, together with competition experiments using cyanide, demonstrates that norharman binds directly to the heme iron of the enzyme as a nitrogen donor ligand. Thus, norharman competes with O2 for the heme iron of the ferrous (active) enzyme, resulting in the observed inhibition. L-Trp and 4-PheImid appear to compete for the heme binding site in the ferric enzyme and display slight negative cooperativity on binding to the ferrous enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

The circuit board found in a commercial musical greeting card is used to supply music for electrochemical cell demonstrations. Similar to a voltmeter, the “modified” musical device is connected to a chemical reaction that produces electricity. The commercial 1 V battery inside the greeting card circuit board can be replaced with an external power source such as a zinc and copper(II) electrochemical cell, a lemon battery or other zinc/proton cell variations, or a commercial solar cell. Directions are given to modify the musical circuit board, to make two types of homemade batteries, and to connect the “modified” musical device to an external power source to create a musical electrical circuit. Unlike a buzzer or flashing light, noticeable variations in music can warn the user of a gradual impending power failure. Students, including the visually impaired and blind, can relate the low volume and the slow tempo of a familiar song with weak or dying batteries and the lack of sufficient power.

same sized pom pons, an increase in the overall physical size of these crystals is illustrated as one proceeds, (left to right) from the simple cubic structure to the body centered cubic structure to the face centered cubic structure. Photo by John B. Zibluk. Figure 2. To keep the edge length for each type of filled cubic cell constant, the radii of the atoms must be different. This can be made visually apparent if different sized pom pons are utilized to construct each type of filled cubic cell. Photo by John B. Zibluk.Figure 3. Different packing arrangements can be demonstrated using different colored pom pons. (a) Triangular layers of pom pons can be arranged (or sewn together) to show how these planes can be stacked with loose pom pons to create hexagonal closepacked and cubic close-packed structures. (b) A loose pom pon can be placed on the top and the bottom of two oppositely pointed (antiparallel) triangular planes to produce a face centered cubic structure. Photo by John B. Zibluk. (a) (b)In general chemistry classes, students are introduced to the ways in which atoms are arranged in cubic crystal structures. Transposing the textbook illustrations into three-dimensional structures is difficult for some students. This transition is easier if a three-dimensional model is available for examination. Models constructed from carved balsawood (1), cut and polished Plexiglas (2), wires soldered to an iron center (3), and reflective glass boxes containing light-emitting diodes (4) can demonstrate several or one specific basic crystallographic unit. A substitute for expensive commercial crystal cage models, which requires less preparation time and dexterity than the above crafted models, is a model constructed of Styrofoam balls and toothpicks. Here Styrofoam balls representing atoms are associated with each lattice point in the unit cells. Similarly, cork balls glued to Plexiglas (5) and marbles that rest in holes cut in stacked Plexiglas shelves (6) have been used to represent atoms. Like the marble model, a cardboard box "theater" model with interchangeable cellophane screens (7) can be constructed to effectively demonstrate the relationship of several neighboring unit cells for different cubic crystal structures.In my general chemistry classes, I have utilized olefin pom pons 1 to illustrate different cubic crystal structures (Fig. 1). Unlike Styrofoam balls that are difficult to paint or not always readily obtainable in a variety of colors, pom pons come in assorted colors. These durable pom pons also are easier to store without breakage. Assembly does not require special cutting skills or long preparation times. The olefin material is coarse enough to allow the pom pons to be stacked upon one another or be positioned side by side without rolling off the table. No glue is needed, so the pom pons can be reused or rearranged to make additional crystal structures. For added stability, it is easy to sew the pom pons together.An additional advantage of this pom pon model over most of the previously described models...

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