Effects of Light on Dopamine Metabolism in the Chick Retina

The effect of prolonged exposure to light on the activity of dopaminergic neurons and dopamine (DA) metabolism of chick retinae was investigated. alpha-Fluoromethyldopa, a potent and specific irreversible inactivator of aromatic amino acid decarboxylase, was used to assess DA turnover after inhibition of synthesis, and also to assess in vivo tyrosine hydroxylase activity by dihydroxyphenylalanine accumulation. After 48 h of light exposure, retinal DNA in 12-day-old chicks was about 30% higher (p less than 0.005) whereas dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were elevated two to three times (p less than 0.005) the level of controls kept in the dark for the same period. DA turnover was about twofold faster in the light (t 1/2 = 31 min) than in the dark (t 1/2 = 65 min). Tyrosine hydroxylase, assayed in vitro with saturating levels of cofactor and substrate, increased by about 50% after light exposure. The apparent tyrosine hydroxylase activity in vivo was approximately sixfold higher in the light than the dark. These results are interpreted and discussed in terms of the regulation of DA synthesis, and the use of DOPAC and HVA as indices of DA function in the retina.     

A simple sensitive radioreceptor assay for calcium antagonist drugs

A radioreceptor assay for calcium channel antagonist drugs described here is based on the ability of these drugs to affect ³H-nitrendipine binding to calcium channels. All the known calcium channel antagonists may be assayed in this manner. The assay can detect 10–100 nM (4 – 40 ng/ml) nimodipine, 10–100 nM (3.5 – 35 ng/ml) nifedipine, 3–30 μM (1.2 – 12 μm/ml) prenylamine, 0.1 – 1.0 μM (49 – 490 ng/ml) verapamil and 3–30 μM (1.2 – 12 μg/ml) diltiazem. These values cover the range of concentrations of calcium channel antagonists that are clinically important. As the radioreceptor assay detects active metabolites as well as the parent drugs, it should prove a useful adjunct in cardiovascular therapy. The method is more reproducible, simpler and less expensive than other methods such as high pressure liquid chromatography.     

Elastase-type activity of human serum. Its variation in chronic obstructive lung diseases and atherosclerosis

Human serum was found to contain enzyme activities hydrolyzing succinyl trialanine paranitroanilide and 3H-kappa-elastin Sepharose substrates. Both types of activities could be partly abolished by serine active site titrants (phenylmethanesulfonylfluoride, diisopropylphosphorofluoridate) and partly by neutral chelating agents (EDTA; 1-10-phenanthroline). The combination of phenylmethanesulfonylfluoride and EDTA gave a complete inhibition of human serum elastase-type activities indicating the presence of at least two different types of elastases (serine and metalloproteases) in human serum. In nonsmokers, the average serum elastase-type activity on succinyl trialanine paranitroanilide was found equal to 78.1 ng/ml porcine pancreatic elastase equivalents and on 3H-kappa-elastin sepharose beads equal to 688.8 ng/ml. No statistically significant differences were observed in elastase levels in the sera of individuals presenting clinical symptoms of atherosclerosis. The sera of patients suffering from chronic obstructive lung diseases contained, however, higher amounts of elastase-type activities, respectively equal to 237.2 ng/ml on succinyl trialanine paranitroanilide and 1,096 ng/ml on 3H-kappa-elastin Sepharose beads and was quantitatively significant when compared with control subjects.     

Effect of salts on C-phycocyanin

The effect of a number of inorganic anions on the quaternary structure of C-phycocyanin has been investigated by fluorescence polarization. Dissociation to monomer occurred in the order: SCN⁻ > ClO₄⁻ > NO₃⁻ > Br⁻ > Cl⁻. These results suggest that hydrophobic interactions are important in the hexamer-monomer equilibrium of C-phycocyanin.     

Charge effects in the sedimentation of polyelectrolytes

The theory for sedimentation of macromolecular polyelectrolytes in solutions of low-ionic strength has been modified for the case of a supporting low molecular weight electrolyte possessing a partial specific volume close to unity. The final equations simplify greatly, allowing sedimentation data to be plotted in a linear fashion. These data then may be readily extrapolated to infinite dilution, yielding a value, S^o, simply related to size and shape. From the initial slope of such plots, the net charge on the macro-molecular polyelectrolyte may be determined. It is suggested that tetramethyl-ammonium chloride may prove to be a satisfactory supporting electrolyte for such studies.