Despite its growing use as a radiological indicator of neuronal viability, the biological function of N-acetylaspartate (NAA) has remained elusive. This is due in part to its unusual metabolic compartmentalization wherein the synthetic enzyme occurs in neuronal mitochondria whereas the principal metabolizing enzyme, N-acetyl-L-aspartate amidohydrolase (aspartoacylase), is located primarily in white matter elements. This study demonstrates that within white matter, aspartoacylase is an integral component of the myelin sheath where it is ideally situated to produce acetyl groups for synthesis of myelin lipids. That it functions in this manner is suggested by the fact that myelin lipids of the rat optic system are well labeled following intraocular injection of [ 14 C-acetyl]NAA. This is attributed to uptake of radiolabeled NAA by retinal ganglion cells followed by axonal transport and transaxonal transfer of NAA into myelin, a membrane previously shown to contain many lipid synthesizing enzymes. This study identi®es a group of myelin lipids that are so labeled by neuronal [ 14 C]NAA, and demonstrates a different labeling pattern from that produced by neuronal [ 14 C]acetate. High performance liquid chromatographic analysis of the deproteinated soluble materials from the optic system following intraocular injection of [ 14 C]NAA revealed only the latter substance and no radiolabeled acetate, suggesting little or no hydrolysis of NAA within mature neurons of the optic system. These results suggest a rationale for the unusual compartmentalization of NAA metabolism and point to NAA as a neuronal constituent that is essential for the formation and/or maintenance of myelin. The relevance of these ®ndings to Canavan disease is discussed.

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Supramolecular host-guest interaction of neutral and cationic (protonated) forms of two boron-dipyromethane (BODIPY)-benzimidazole (mono- and di-benzimidazole) conjugate dyes with the macrocyclic host cucurbit[7]uril (CB7) has been investigated using photophysical and density functional theory studies. Expectedly, cationic forms of the dyes show exceptionally stronger binding than that of the neutral forms with CB7, which can be ascribed to the strong ion-dipole interaction between the positive charge of the dye and the highly polarizable carbonyl portals of the host. The formation of dye-host inclusion complexes is supported by the significant changes in the photophysical properties and longer rotational relaxation times of the dye in the presence of CB7. Job's plot studies indicate the formation of a 1:1 inclusion complex for the mono and a 1:2 inclusion complex for the dibenzimidazole BODIPY dyes. Quantum chemical calculations are in good agreement with the inferences outlined from photophysical measurements. Findings from the studied dye-CB7 systems are of direct relevance to applications such as drug delivery, aqueous dye lasers, sensors, and so on.

Developing sensitive and selective near-infrared fluorescent bio-probes for serum albumin detection is an ambitious and highly rewarding task. Herein, we report a styryl based fluorophore for serum albumin detection, which displays an exceptional turn-on emission enhancement of ∼500 fold, the highest reported so far in the near-infrared region, and more importantly enables quantification of albumin in the complex serum matrix.

Transfer RNA (tRNA) has been demonstrated to be present in axons of both invertebrates and the higher vertebrates, but nothing is known of its role in the metabolism of the axon. The present experiments were performed to determine whether tRNA functions in axons as a participant in post-translational protein modification of endogenous proteins. RNA was extracted from the axoplasm of squid giant axons and incubated with a variety of 3H-amino acids, aminoacyl-tRNA synthetases (obtained from squid optic lobe), and an appropriate reaction mixture. All of the amino acids tested were bound to an RNA fraction, but this reaction did not occur when samples were incubated in the presence of ribonuclease or in the absence of axoplasmic RNA. When radioactive RNA was chromatographed by polyacrylamide gel electrophoresis, the radioactivity comigrated with known tRNA markers, suggesting the presence of 3H-aminoacylated tRNA. Aminoacylation of RNA could also be demonstrated by incubating fresh axoplasm with labeled amino acids and a reaction mixture, minus exogenous aminoacyl-tRNA synthetases. These findings indicate the presence in axoplasm of a variety of species of aminoacyl-tRNAs as well as their corresponding synthetase enzymes. In the latter experiment no radioactivity was found associated with the protein fraction. This was also the finding when 3H-aminoacylated tRNA was either injected directly into the axon or incubated with extruded axoplasm. Thus, under the conditions described above, there is no evidence of transfer of amino acids from tRNA to proteins. In other experiments, axoplasm was pooled to a volume of 50 to 100 microliters, homogenized gently, and centrifuged at 150,000 X g for 1 hr. Some of the high speed supernatant was incubated with labeled amino acids and an appropriate reaction mixture, and the remainder was passed through an S-200 Sephacryl column before incubation with the same reaction mixture. There was no incorporation of amino acids into protein in the high speed supernatant fraction. However, in the S-200 purified fraction 3H-labeled Arg, Lys, Tyr, Leu, and Asp were all incorporated into proteins in amounts of 44, 30, 7, 5 and 3.5 times heat-inactivated controls. The reaction is not inhibited by Ca2+ or Ca2+-activated proteases, but appears to be dependent on the presence of tRNA. The addition of amino acids to protein is not protein synthesis since the reactions occurred in a partially purified fraction of the 150,000 X g supernatant, a fraction devoid of ribosomes and free amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)