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PubMed1994

Conformational preferences of oligopeptides rich in alpha-aminoisobutyric acid. III. Design, synthesis and hydrogen bonding in 3(10)-helices.

Two sterically constrained peptides [iBoc-Aib-Aib-Aib-DkNap-Leu-Qx-Ala-Aib-Aib-Fl, (Dk4Qx6[7/9]) and iBoc-Aib-Aib-Aib-DkNap-Leu-Aib-Ala-Aib-Aib-Fl, (Dk4[7/9])] containing alpha-aminoisobutyric acid (Aib) and Aib-class amino acids in conjunction with selected mono-alpha-alkyl amino acids were synthesized by an optimized TBTU/HOBt procedure. The use of Aib-class amino acids (e.g. DkNap and Qx), defined and discussed here, gives rise to the same overwhelmingly 3(10)-helical backbone conformation as that provided by simpler Aib-rich peptides and homopeptides. The synthetic alpha,alpha-dialkylamino acids (DkNap, Qx) are aromatic homologues of the known alicyclic variants of Aib, the Ac5c and Ac6c amino acids. Two new organic solubilizing groups for peptides, iBoc and 2-methoxyethylamine, are introduced. The 1H nuclear magnetic resonance analyses of the Dk4[7/9] and Dk4Qx6[7/9] peptides demonstrate the unambiguous 3(10)-helical hydrogen bonding pattern of these peptides, confirming the design objective of these sequence patterns containing greater than 50% Aib and Aib-class composition.

Amino Acid Sequence↗
PubMed1997

Synthesis of achatin-I (Gly-D-Phe-L-Ala-L-Asp) analogs having dehydrophenylalanine or aminoisobutyric acid residue at position 2, and their effects on Achatina giant neurons.

1. Achatin-I (Gly-D-Phe-L-Ala-L-Asp), a neuroactive tetrapeptide having a D-phenylalanine residue, has been proposed to be an excitatory neurotransmitter of Achatina giant neurons. It was revealed that the D-Phe2 residue is essential for bioactivity of achatin-I, which seems to adopt beta-turn conformation. In the present study, in order to investigate the structure-activity relationships of achatin-I and its derivatives, the two highly constrained analogs of achatin-I, [delta ZPhe2]achatin-I (Gly-delta ZPhe-L-Ala-L-Asp) (delta ZPhe: (Z)-alpha,beta-dehydrophenylalanine) and [Aib2]achatin-I (Gly-Aib-L-Ala-L-Asp) (Aib: alpha-aminoisobutyric acid), were synthesized, and their effects on the two identifiable Achatina giant neuron types, PON (periodically oscillating neuron) and v-RCDN (ventral-right cerebral distinct neuron), were examined in comparison with those of achatin-I under voltage clamp. 2. Achatin-I (n = 6), ejected onto the neurone by brief pneumatic pressure (2 kg/cm2, 400 ms, 10(-3) M, at 10-min intervals), produced an inward current (Im) on PON. The Iin value (mean +/- SEM) was 0.44 +/- 0.03 nA. The interval between the achatin-I ejection and the Iin peak was 14.74 +/- 3.15 s (n = 6). [delta ZPhe2]achatin-I (n = 6) and [Aib2]achatin-I (n = 6) had no effect on this neuron type. 3. On the other hand, achatin-I (n = 10) and [delta ZPhe2]-achatin-I (n = 10), ejected by brief pressure, produced an Iin on v-RCDN. The Iin values were 0.85 +/- 0.07 nA for achatin-I and 0.48 +/- 0.05 nA (p < 0.01, compared with that of achatin-I by Student's t-test for paired data) for [delta ZPhe2]achatin-I. The intervals between the compound ejection and the Iin peak were 5.95 +/- 0.33 s for achatin-I and 8.70 +/- 0.81 s (p < 0.05, compared with that of achatin-I) for [delta ZPhe2]achatin-I. [Aib2]achatin-I (n = 10) had no effect on this neuron type.

Animals↗
PubMed1992

Effect of prolactin on alpha-aminoisobutyric acid uptake in mouse mammary gland explants.

Studies were carried out to characterize the effect of prolactin (PRL) on amino acid uptake into mammary gland explants derived from 12- to 14-day pregnant mice. PRL approximately doubles the rate of uptake of alpha-aminoisobutyrate (AIB), arginine, and hydroxyproline but has no effect on the intracellular accumulation of unincorporated leucine. PRL increases the apparent maximum velocity of AIB uptake from 0.16 to 0.43 nmol.l intracellular water-1.min-1. No effect of PRL, however, on the apparent Michaelis constant (0.75 mM) of AIB uptake was observed. The onset of the PRL stimulation of AIB uptake occurs 4-5 h after PRL addition to the cultured mammary tissues. The lowest stimulatory concentration of PRL on AIB uptake is 5-10 ng/ml, and a maximum response is achieved with 75 ng/ml. The action of PRL on AIB uptake requires both ongoing RNA and protein synthesis, since puromycin (50 micrograms/ml), cycloheximide (5 micrograms/ml), and actinomycin D (1 microgram/ml) abolished the PRL response.

Amino Acids↗
PubMed1979

[Effect of different oxygen pressure levels on the transport of alpha-aminoisobutyric acid in myocardial cell cultures].

The activity of aminoacid transport, as measured by alpha-aminoisobutyrate uptake, has been studied in confluent myocardial cell cultures exposed to different oxygen tensions. The results obtained indicate that the rate of cellular uptake and accumulation of the inert aminoacid increase with time as the fraction of oxygen is reduced. When alpha-aminoisobutyrate was added in presence of all other aminoacids of the medium, the effect of oxygen was also evident, suggesting a mechanism which overcomes the competitive action of the other aminoacids assigned to the same transport system of alpha-aminoisobutyrate (A system). The modulation of aminoacid transport activity may represent one of the possible mechanisms by which environmental oxygen affect the rate of cellular protein synthesis.

Aminoisobutyric Acids↗