Human liver alcohol dehydrogenase catalyzes the NAD+-dependent oxidation of alcohols. Isoenzymes are produced in liver by five different genes, two of which are polymorphic. We have studied the three beta beta isoenzymes produced at ADH2 because they exhibit very different kinetic properties and they appear with different frequencies in different racial populations. The beta 3 beta 3 isoenzyme which appears in 25% of black Americans was purified to homogeneity, and conditions were found to stabilize this labile isoenzyme. The comparison of substrate specificity among beta beta isoenzymes for primary straight-chain alcohols indicates that there is a positive correlation between Vmax/KM and the log octanol/water partition coefficient for alcohols with beta 2 beta 2 and beta 3 beta 3 but not with beta 1 beta 1. Methyl substitutions at C1 or C2 of these alcohols reduce the catalytic efficiency with all three isoenzymes. The KM and Ki values of beta 3 beta 3 for NAD+ and NADH are substantially higher than values for beta 1 beta 1 or beta 2 beta 2. The Vmax of beta 3 beta 3 ethanol oxidation is 90 times that of beta 1 beta 1. Sequencing of the beta 3 subunit and gene indicates that the polymorphism results from a single amino acid exchange of Cys-369 in beta 3 for Arg-369 in beta 1 and beta 2 [Burnell et al. (1987) Biochem. Biophys. Res. Commun. 146, 1227-1233]. In horse alcohol dehydrogenase and beta 1 beta 1, the guanidino group of Arg-369 is thought to stabilize the NAD(H)-enzyme complex by bonding to one of the pyrophosphate oxygens.(ABSTRACT TRUNCATED AT 250 WORDS)
Polymer synthesis has a limited inclusion in most organic chemistry lecture curricula, so emphasizing the concepts of polymer chemistry in a laboratory setting gives students hands-on experience in new content and broadens the scope of the class. The details and outcomes of a robust and well-developed laboratory procedure for the synthesis of a crosslinked epoxy network polymer are described. This experiment has been a part of a first-semester, introductory undergraduate organic chemistry laboratory curriculum for more than two decades and has positively impacted over eight hundred students. The experiment had the unique aspect that students cured the resin in a round, seven-centimeter mold, forming a hardened epoxy disk. This disk, or medallion, was decorated in two different ways: first, a design was etched into the mold before curing to form a permanent imprint; second, the final epoxy medallion was decorated, post-cure, with colored permanent markers and glitter glue. After this laboratory experiment, students took home a durable ornament as a memento of their first-semester organic chemistry laboratory course.
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