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The destruction of serine and threonine thiohydantoins during the sequence determination of peptides by 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate.

1. A mechanism for the destruction of serine and threonine thiohydantoins during protein sequence analysis by the Edman-type degradation is proposed. The mechanism begins with the dehydration of serine and threonine side chains (at the cyclization stage) which occurs mainly in anhydrous acid solution. The dehydrated derivatives finally polymerize by way of the reactive methylene group (enamine) to form polymers with various molecular weights. In aqueous acid solution, the dehydrated thiohydantoins of serine and threonine undergo hydration (according to the Markovnikov rule) and ring fission, which leads to the irreversible breakdown of thiohydantoin ring. The serine derivative shows a much greater tendency to undergo these side-reactions than the threonine derivative. 2. In the presence of oxygen, the alkaline hydrolysis of amino acid thiohydantoins goes through an oxidation-deamination reaction at the C-N bond of the thiohydantoin ring and leads to the formation of thiourea derivative and keto acids. This reaction mechanism accounts for the low recoveries of amino acid obtained from the alkaline hydrolysis of amino acid thiohydantoins.

Amino Acid Sequence↗

Metaphit, an isothiocyanate analog of PCP, induces audiogenic seizures in mice.

Metaphit induces audiogenic seizures in mice. The most severe clonic/tonic seizures occur 18-24 h after metaphit administration. After 48 h the incidence of the seizure episodes begin to diminish. These audiogenic seizures can be prevented by the administration of either PCP or MK-801 24 h after metaphit and 30 min prior to audio stimulation. These seizures may be due to a modulation of the PCP recognition site by metaphit which results in an enhanced probability that the NMDA/PCP ion channels are open.

Acoustic Stimulation↗

Acylation of sigma receptors by Metaphit, an isothiocyanate derivative of phencyclidine.

Pretreatment of guinea pig brain membranes with 1-[1-(3-isothiocyanatophenyl)cyclohexyl]piperidine (Metaphit) caused irreversible and differential inhibition of ligand binding to sigma (sigma) receptors. The concentration of Metaphit required to produce 50% inhibition of binding of [3H]1,3-di-o-tolylguanidine ([3H]DTG), [3H](+)-3-(3-hydroxy-phenyl)-N-(1-propyl)piperidine ([3H](+)-3-PPP), and [3H](+)-N-allylnormetazocine ([3H](+)-SKF 10,047) to sigma receptors was 2, 10 and 50 microM, respectively. This compares to a value of 10 microM for inhibition of [3H]1-[1-(2-thienyl)cyclohexyl]piperidine [( 3H]TCP) binding to phencyclidine (PCP) receptors. While Metaphit was an irreversible, non-competitive inhibitor at PCP receptors, this compound produced irreversible, competitive inhibition at sigma receptors.

Acylation↗