The biotinylated probe, 3-azido-10-(4-(4-biotinyl-1-piperazinyl)butyl)phenothiazine, was used to examine the phenothiazine binding domains in calmodulin (CaM) by photolabeling. This phenothiazine, synthesized from 3-azido-10-(4-(1-piperazinyl)butyl)phenothiazine and d-biotinyl tosylate, inhibited the CaM-mediated activation of phosphodiesterase (PDE) with an I50 of 12.5 (+/- 2.8) microM. Photolabeling of CaM produced covalent adducts in excellent yield (32%) in a light- and Ca2+-dependent manner. Studies performed over a range of drug concentrations suggested a 2:1 stoichiometry for the binding of the phenothiazine probe to CaM. Limited trypsin digestion and purification of the resulting fragments by either SDS-PAGE or HPLC provided two principal phenothiazine-containing peptides. Amino acid composition and sequence analyses performed on these two peptides established that both the N- and C-terminal domains in CaM, particularly the regions amino terminal to Ca2+-binding loops 1 and 3, were modified by the photoactivated phenothiazine derivative. These data, particularly for the C-terminal domain, are in excellent agreement with the X-ray structure analysis of a 1:1 CaM-trifluoperazine complex.

The structures of three nitro-substituted phenothiazines [1,3,4-trifluoro-2-nitrophenothiazine, 10-(4-chlorobutyl)-1,3,4-trifluoro-2-nitrophenothiazine and 10-(4-chlorobutyl)-3-nitrophenothiazine] have been determined. The first of these red compounds forms infinite stacks in the solid state, in which donor and acceptor regions of the approximately planar molecules alternate. The molecules of the other two compounds, which have folded, or 'butterfly', conformations in the solid state, do not form stacks, presumably because the bulky chlorobutyl substituents cannot be accommodated. The very dark color of solid 3-nitrophenothiazine suggests the presence of extended molecular stacks, but crystals suitable for a structure determination could not be obtained.

Various photoactive phenothiazines were synthesized that possessed a 2-azido, 3-azido, 2-benzoyl, or 1,3,4-trifluoro-2-azido functionality in combination with various modifications of the N-alkyl side chain. These phenothiazines were evaluated for their ability to inhibit the calmodulin-mediated activation of phosphodiesterase (PDE). All were active in inhibiting the action of calmodulin (CaM), but those possessing either a 3-azido and a 4-(4-methyl-1-piperazinyl)butyl side chain or a 2-benzoyl group and 3-(dimethylamino)propyl side chain proved to be most active (I50 = 14 +/- 3 microM and 7 +/- 1 microM, respectively) when compared to the known inhibitor, chlorpromazine (CPZ, I50 = 30 microM). Calmodulin was photolabeled with ca. 35% efficiency in a light- and calcium-dependent fashion using a radiolabeled analog, 3-azido-10-(4-(4-[14C]methyl-1-piperazinyl)butyl)phenothiazine, of one of these compounds. Competition studies using this radiolabeled analog and CPZ were consistent with binding to one or both of the hydrophobic binding pockets of CaM.

Typically, hydrophobic residues in proteins are found on the interior of the tertiary structure minimizing interactions with water. Many proteins function by exposing hydrophobic faces to the solvent. The molecule 1‐anilinonaphthalene‐8‐sulfonic acid (1,8‐ANS) will fluoresce exclusively in presence of hydrophobic interactions allowing investigation of exposed pockets in proteins. Two separate investigations with ANS and the proteins calmodulin and lysozyme are outlined. Calmodulin in the presence of calcium exposes two hydrophobic pockets which are accessible to ANS increasing the fluorescence signal compared to the absence of calcium. Lysozyme in the presence of varying the concentration of urea and ANS will produce a fluorescence maximum indicating a conformational structure exposing the hydrophobic core to solvent called the molten‐globule state. These investigations are intended for an introductory laboratory in biochemistry.

Green fluorescent protein (GFP) has become increasingly useful in both research and educational settings because of its ease of detection. Our goal was to develop a low tech way in which to use GFP to demonstrate the effects of denaturants on protein folding. This technique would be especially practical for high schools and small colleges where access to specialized equipment is limited. Crude lysate from E. coli cells expressing GFP was used to monitor the effects of SDS and urea on fluorescence and hence folding of GFP. We first confirmed that GFP fluorescence could be observed visually by excitation with a UV light pen (Bio‐Rad®). We then denatured the protein with 5M urea or 1% SDS and again monitored fluorescence. We were unable to detect fluorescence as expected for denatured GFP. We confirmed these results by performing an unfolding curve with concentrations of urea between 1M and 5M and SDS between 0.25% and 1%. Although we were unable to visually detect a significant change in fluorescence at the intermediate concentrations of urea and SDS, we were able to observe differences between fully folded GFP and unfolded GFP using a UV light pen.