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The interaction of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) with cytochrome P450 2D6 (CYP 2D6) was analyzed via nuclear magnetic resonance spectroscopy to characterize the mode of binding of the neurotoxin. The mode of binding of MPTP with CYP 2D6 and the resulting products of the interaction were altered by the addition of human nicotinamide reduced adenine dinucleotide phosphate-cytochrome P450 reductase. Furthermore, the interaction between the two enzymes induced an allosteric change in the active site of CYP 2D6.

The putative response regulator of nisin biosynthesis, the nisR gene product, was discovered to be an essential part of the induction mechanism of the control of nisin immunity. This protein is a component of a two-part regulatory system which controls the expression of genes needed in nisin immunity and biosynthesis. Findings revealed that the 12 amino-terminal residues of the molecule are a minimum requirement for induction, with an intact ring A being a vital part.

Substitution of dehydroalanine residue at position 5 in nisin by alanine leaves nisin's bacterial growth inhibiting activity unaffected. However, it reduces its activity as an inhibitor of the outgrowth of spores. The bacterial growth and spore outgrowth inhibitive activities of both nisin and subtilin are based on different structure-activity relationships and therefore the two activities arise from different molecular mechanisms. The presence of dehydroalanine residue at position 5 is unnecessary for inhibiting Lactococcus lactis and Micrococcus luteus growth.

The human cytochrome P450 2D6 (P450 2D6) was prepared by a baculovirus expression system, and then purified at 4 degrees C. A model of the complex of codeine with P450 2D6 was designed by combined homology modeling and distance restraints from paramagnetic relaxation calculations. Homology modeling involved the alignment of the P450 2D6 sequence against the multiple sequence and modification by Cameleon. In the model, the Asp 301 anionic residue forms an ion pair with the basic nitrogen of codeine.

Examination of a mutant of Lactobacillus casei dihydrofolate reductase, D26N, having asparagine for active site aspartic acid residue, by NMR and optical spectroscopy reveals that the mutation exerts little influence on the structure of the enzyme. Substitution exerts little influence on coenzyme, substrate and inhibitor binding. Isotope studies reveal that hydride ion transfer is the rate-limiting step for the mutant enzyme catalysis.

Site-directed mutation combined with isotope-edited 1H nuclear magnetic resonance spectroscopy was used to analyze chloramphenicol acetyltransferase (CAT) complexed with diacetyl chloramphenicol. 1H signals were detected from the methyl groups of the acetyl substituents of the substrate. Molecular modeling showed that these methyl groups interact with a number of residues in the chloramphenicol-binding region of CAT. Site-directed mutation revealed that the tyrosine residue at position 25 of CAT is close to the acetyl substituent at position 3 of the substrate.