The solid-state catalytic synthesis of tritium labeled amino acids, peptides and proteins.

New catalytic reaction between a solid bioorganic compound and activated spillover tritium (ST), based on High-temperature Solid-state Catalytic Isotopic Exchange (HSCIE) was examined. The HSCIE mechanism and determination of the reactivity of hydrogen atoms in amino acids, peptides and proteins was investigated. Quantum mechanical calculations of the reactivity of hydrogen atoms in amino acids in the HSCIE reaction were done. The carbon atom with a greater proton affinity undergoes a greater exchange of hydrogen for tritium in HSCIE. The electrofilic nature of spillover hydrogen in the reaction of HSCIE was revealed. The isotope exchange between ST and the hydrogen of the solid organic compound proceeds with a high degree of configuration retention at the carbon atoms. The HSCIE reaction enables to synthesize tritium labeled proteins with a specific activity of 20-30 mCi/mg and kept biological activity.

The neurotropic activity of a structural analog of ACTH(5-7).

The tripeptide glutamyl-arginyl-proline (ERP) mimicking some structural features of the N-terminal fragment of adrenocorticotropic hormone, ACTH(5-7), has been synthesized. In contrast with ACTH fragments, ERP (0.015-0.15 mg/kg; intraperitoneal injection) hindered the formation of food-reinforced task in adult albino male rats. Besides, ERP caused a rapid inhibition of the previously formed conditioned task. Similar doses of ERP changed orientative-trying reaction and emotional behavior in rats in the 'open field' test. ERP at a dose of 0.15 mg/kg administered prior to the injection of 0.5 mg/kg ACTH(1-39) prevented increases in locomotor activity normally induced by this hormone. Thus, ERP disrupts learning, impairs performance of acquired task and blocks behavioral effects of ACTH and its fragments.

Degradation of ACTH/MSH(4-10) and its synthetic analog semax by rat serum enzymes: an inhibitor study.

Degradation of the behaviorally active peptide ACTH/MSH(4-10) and its synthetic analog semax was studied in serum in the presence of several specific peptidase inhibitors. Bestatin and puromycin were used to inhibit aminopeptidase activity, lisinopril for angiotensin-converting enzyme, phosphoramidon for neutral endopeptidase 24.11, and Z-Pro-prolinal for prolyl endopeptidase. Bestatin inhibited up to 66%, puromycin about 33%, and lisinopril about 15% of total degrading activity against both ACTH/MSH(4-10) and semax. Involvement of neutral endopeptidase and prolyl endopeptidase in hydrolysis of the two peptides was less definitive. These studies showed that aminopeptidases and angiotensin-converting enzyme are responsible for the major part of the hydrolysis of ACTH/MSH(4-10) and semax in rat serum.

Use of tetrabutylammonium salts of amino acids in peptide synthesis.

Tetrabutylammonium (TBA) salts of amino acids and peptides have increased solubility, as compared with that of alkali metals salts, in organic solvents. We have compared the reaction rates for tripeptide formation in methylene chloride from Boc-Gly-Phe activated with various phenols, N-oxysuccinimide and azide, and TBA-salt of tryptophan, as well as Trp-OCH3. H-Trp-O-.TBA+ as an amino component significantly accelerates the rate of reaction. Although a significant degree of racemization has been found, the use of TBA-salt of amino acids and peptides is justified in many cases due to high conversion rates.

Entry of the synthetic ACTH(4-10) analogue into the rat brain following intravenous injection.

In view of known central effects of N-terminal ACTH fragments, a possibility of their entry into the brain was studied. Rat blood and brain extracts after intravenous injection of the tritiated synthetic ACTH(4-10) analogue, Met-Glu-His-Phe-Pro-Gly-Pro, were subjected to a high-performance liquid chromatographic analysis. At two time points the labelled peptide was detected in brain extracts. The brain to blood ratios of peptide content in brain and blood were found to be significantly higher than those calculated for a distribution of labelled bovine serum albumin in rat brain capillaries and blood. This strongly suggests that this peptide penetrates into the brain tissues, its quantity not exceeding 0.01% of dose injected. Peptide diffusion through the vascular epithelium of brain capillaries could account for the data obtained.

N-terminal degradation of ACTH(4-10) and its synthetic analog semax by the rat blood enzymes.

Degradation of a regulatory peptide ACTH(4-10) and its synthetic analog semax in rat blood and serum was studied using high-performance liquid chromatography. About one third to one half of the serum degrading activity could be ascribed to bestatin-sensitive aminopeptidase which cleaved first and second N-terminal residues Met and Glu producing relatively stable intermediates. Comparable areas under the degradation/accumulation curves for intact peptides and intermediates implied that the latter can contribute to effects of intact peptides. Semax turned out to be more stable than ACTH(4-10) against the action of other enzymes that took part in degradation.