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Notes: We have used the z-scan technique at a wavelength (532 nm) near the transmission window of bulk gold to measure the nonlinear absorption coefficient of continuous approximately 50-Å-thick gold films, deposited onto surface-modified quartz substrates. For highly absorbing media such as metals, we demonstrate that determination of either the real or imaginary part of the third-order susceptibility requires a measurement of both nonlinear absorption and nonlinear refraction, i.e., both open- and closed-aperture z scans must be performed. Closed-aperture z scans did not yield a sufficient signal for the determination of the nonlinear refraction. However, open-aperture z scans yielded values ranging from β=1.9×10−3 to 5.3×10−3 cm/W in good agreement with predictions which ascribe the nonlinear response to a Fermi smearing mechanism. We note that the sign of the nonlinearity is reversed from that of gold nanoparticle composites, in accordance with the predictions of mean field theories. © 1999 American Institute of Physics.

Notes: Abstract: S-Adenosylmethionine is an essential ubiquitous metabolite central to many biochemical pathways, including transmethylation and polyamine biosynthesis. Reduced CSF S-adenosylmethionine levels in Alzheimer's disease have been reported; however, no information is available regarding the status of S-adenosylmethionine or S-adenosylmethionine-dependent methylation in the brain of patients with this disorder. S-Adenosylmethionine concentrations were measured in postmortem brain of 11 patients with Alzheimer's disease. We found decreased levels of S-adenosylmethionine (−67 to −85%) and its demethylated product S-adenosylhomocysteine (−56 to −79%) in all brain areas examined (cerebral cortical subdivisions, hippocampus, and putamen) as compared with matched controls (n = 14). S-Adenosylmethionine and S-adenosylhomocysteine levels were normal in occipital cortex of patients with idiopathic Parkinson's disease (n = 10), suggesting that the decreased S-adenosylmethionine levels in Alzheimer's disease are not simply a consequence of a chronic, neurodegenerative condition. Reduced S-adenosylmethionine levels could be due to excessive utilization in polyamine biosynthesis. The severe reduction in levels of this essential biochemical substrate would be expected to compromise seriously metabolism and brain function in patients with Alzheimer's disease and may provide the basis for the observations of improved cognition in some Alzheimer's patients following S-adenosylmethionine therapy.

Notes: Autonomic activity was recorded from 16 male subjects as they read sexually stimulating material. The resulting physiological response patterns included increases in systolic and diastolic blood pressures, palmar conductance and number of galvanic skin responses. Heart and respiration rates remained relatively constant, and there was some indication of peripheral vasodilatation subsequent to initial constriction. The results suggest a differential change in the activity of both branches of the autonomic nervous system, in which neither the parasympathetic nor the sympathetic nervous system may be considered dominant.

Notes: Phosphocholine is a precursor for phosphatidylcholine or it may be hydrolysed to choline. Choline can be oxidized to form the compatible osmolyte glycine betaine which is accumulated by many plants under conditions of osmotic stress. In Spinacia oleracea phosphocholine is synthesized by 3 sequential N-methylations of phosphoethanolamine with the first step catalysed by the enzyme phosphoethanolamine N-methyltransferase (EC 2.1.1.103). This enzyme has been partially purified 5400-fold from spinach leaves using a combination of ammonium sulphate fractionation, followed by chromatographic separations on DEAE-Sepharose, phenyl-Sepharose, Ω-aminohexyl-agarose, Mono Q and adenosine-agarose. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) separation and silver-staining of the final preparation revealed several polypeptides present, only one of which with an estimated molecular mass of 54 kDa could be photoaffinity cross-linked to the substrate [3H] S-adenosyl-l-methionine. HPLC gel permeation chromatography was used to obtain an estimate for the native molecular mass of 77 kDa. Enzyme activity was optimal at pH 7.8 in HEPES-KOH buffer, it was inhibited by S-adenosyl-l-homocysteine, phosphocholine, phosphate, Mn2+ and Co2+ but not by ethanolamine, methylethanolamine, dimethylethanolamine, choline, glycine betaine or Mg2+. Using phosphoethanolamine as substrate, the final preparation had a specific activity of 189 nmol mg−1 protein min−1. The reaction products were identified and their relative abundance estimated following separation by TLC as phosphomethylethanolamine (87%), phosphodimethylethanolamine (10%) and phosphocholine (2%). Thus, a highly purified preparation of phosphoethanolamine N-methyltransferase was shown to catalyse 3 successive N-methylations of phosphoethanolamine. Photoaffinity cross-linking of proteins extracted from leaves of spinach followed by SDS-PAGE and autoradiography shows that a 54-kDa radiolabelled polypeptide was more prominent in extracts from salinized plants and barely visible in extracts from plants exposed to prolonged dark periods, a pattern which corresponds to the salt and light-responsive changes in phosphoethanolamine N-methylating activity. Thus, the production of phosphocholine for glycine betaine accumulation in spinach can be mediated by a single phosphobase N-methyltransferase which is more abundant in salt-stressed plants.