Chemistry of the phenanthrenequinone (PEQ) test for monosubstituted guanidines

The alkylguanidine-detecting reagent phenanthrenequinone (PEQ) was found to give, in addition to the known fluorescent 2-amino-1H-phenanthro-[9,10-d]-imidazole, the aldehyde corresponding to the alkyl substituent. Benzylguanidine and PEQ gave benzaldehyde and the fluorescent compound; guanidoacetic acid and PEQ gave formaldehyde and a trace of glyoxylic acid; and arginine and PEQ gave low yields of glutamic acid and agmatine as well as ornithine and citrulline.     

Quantitative determination of monosubstituted guanidines: A comparative study of different procedures

Analysis of N²-acyl arginine derivatives as well as of arginine analogs lacking in a α-amino function by Weber's modification of the Sakaguchi procedure yielded colored complexes with absorbance values approximately twice that obtained with an equivalent concentration of unmodified arginine. The limitations concerning the applicability of the various modification of the Sakaguchi procedure as well as of fluorimetric assay to the quantitative estimation of a variety of monosubstituted guanidines and proteins are discussed.     

The GABAA receptor family in the mammalian brain

The GABA_A-benzodiazepine receptor protein from bovine brain was purified by affinity chromatography and the subunit composition examined by gel electrophoresis in sodium dodecyl sulfate. Protein staining revealed a doublet at 51–53 kDa, a band at 55 kDa, and a broad band at 57–59 kDa. The 51 and 53 kDa bands co-migrated with the ₁ and ₂ gene products identified by Western blotting with subtype-specific antibodies. These two bands were also photoaffinity labeled by [³H]flunitrazepam, as was a breakdown product at 44 kDa. Partial sequencing of proteolytic fragments of these polypeptides yielded sequences found in all clones, and identified the benzodiazepine binding site within residues 8–297 and probably between 106–297 of ₁; the 44 kDa and 31 kDa bands yielded fragments containing ₃ sequence. The native ₃ polypeptide was identified with subtype-specific antibody at 57 kDa overlapping with the two major bands photolabeled with [³H]muscimol at 55 and 58 kDa. Antisera to a -selective peptide recognized four bands at 60, 58, 57 and 55 kDa. Thus, one can identify 6–8 distinct polypeptides with the possibility of another 4–6 in purified GABA_A receptor proteins, depending on brain region, consistent with the family of gene products suggested by molecular cloning.Special issues dedicated to Dr. Eugene Roberts     

The occurrence of a glycine cleavage system in mammalian brain

A major catabolic route for glycine in liver is its conversion to methylene tetra-hydrofolate (methylene THF), CO₂ and NH₃, catalysed by the glycine cleavage system described by Yoshida and Kikuchi (1970). In view of the role of glycine as a putative neuro-transmitter, the occurrence of this system in mammalian brain was investigated. Our studies demonstrated: (a) that the production of ¹⁴CO₂ from [1-¹⁴C]glycine required the presence of tetrahydrofolate, NAD, dithiothreitol and pyridoxal phosphate in the reaction mixture; (b) that besides CO₂l -serine was the other major product of the reaction; (c) that glyoxylate did not function as an intermediate in this reaction; and (d) that enzymatic activity appeared to be associated with membranes. All of these properties resembled those previously described for the hepatic system.     

The distribution and role of carnitine in the mammalian brain

A differential distribution of carnitine was found in twelve microdissected areas of the frozen canine brain. The cerebellar cortex showed the highest level of carnitine, while the lowest amounts were found in the hippocampus and pons sections of the brain. However, the inability to demonstrate changes in carnitine levels after $\text{in vivo}$ stimulation of the major afferent pathways in the caudate nucleus, and failure to demonstrate K+ stimulated release of carnitine in rat brain slices suggest that carnitine does not have a direct neurotransmitter role in the brain.     

The neuroanatomy of the kisspeptin system in the mammalian brain

The kisspeptin precursor is the protein transcribed from the Kiss-1 gene and the kisspeptins are the peptides that are posttranslationally processed from the precursor. The kisspeptins activate the G-protein coupled receptor GPR54 and are strongly implicated in puberty onset and in regulation of the hypothalamo-pituitary gonadal axis in mammals. Physiological studies have indicated that these effects occur via a direct activation of the GnRH neurons, and at an unknown site in the median eminence or directly on the gonadotropes. Paradoxically, while the function of kisspeptin is relatively well understood, little data are available about the localization of kisspeptin neurons in the brain, and in particular the projection patterns of kisspeptin containing axons implicated in regulation of the hypothalamo-pituitary gonadal axis. This review covers the current information about the localization of kisspeptin neurons in the mammalian brain and discusses the facts and artifacts of the methods of their detection. The available data suggest that kisspeptins are synthesized in neurons in the anteroventral periventricular nucleus and the arcuate nucleus. Both populations are considered to be involved in control of gonadotropes. In addition, kisspeptin nerve terminals and receptors are found in other hypothalamic area suggesting that kisspeptins are involved in regulation of other yet unknown homeostatic or neuroendocrine functions.     

Putrescine catabolism in mammalian brain

In contrast with putrescine (1,4-diaminobutane), which is a substrate of diamine oxidase, monoacetylputrescine is oxidatively deaminated both in vitro and in vivo by monoamine oxidase. The product of this reaction is N-acetyl-gamma-aminobutyrate. The existence of a degradative pathway in mammalian brain for putrescine is shown, which comprises acetylation of putrescine, oxidative deamination of monoacetylputrescine to N-acetyl-gamma-aminobutyrate, transformation of N-acetyl-gamma-aminobutyrate to gamma-aminobutyrate and degradation of gamma-aminobutyrate to CO(2) via the tricarboxylic acid cycle.     

Spectrin subtypes in mammalian brain

Mammalian neural cells contain at least two forms of brain spectrin: brain spectrin (240/235) which is located primarily in the axons and presynaptic terminals of neurons, and brain spectrin (240/235E) which is found in the cell bodies, dendrites and postsynaptic terminals of neurones. Brain spectrin (240/235E) is also found in certain glial cell types. Antibodies against red blood cell spectrin detect only brain spectrin (240/235E), while antibodies against brain spectrin isolated from axonal and synaptic membranes detect brain spectrin (240/235). Previous apparent discrepancies in the literature concerning brain spectrin localization at the light microscope level were undoubtedly due to different laboratories detecting distinct brain spectrin subtypes, based on the particular antibody being utilized for immunohistochemistry. In this review we (1) discuss the data supporting the presence of at least two distinct subtypes of mammalian brain spectrin, (2) explain how these results reconcile previous discrepancies concerning the localization of spectrin within neural cells, and (3) suggest the future implications of these findings.     

A simple molecular mathematical model of mammalian hibernation

A simple model of the dynamics of the body temperature of a hibernating mammal is presented. Our model provides a good match to experimental data, showing the interruption of low-temperature torpor bouts with periodic interbout arousals (IBAs). In this paper we present a mathematical model of the molecules that participate in the initiation, regulation, and maintenance of the hibernating state. This model can be used to describe the role of regulatory molecules, signal transducers, downstream target enzymes, structural proteins, or metabolites. Because many of the biochemical mechanisms are unknown, this is a preliminary and largely phenomenological model that we hope will inspire further investigation.