L-Alanyl-L-Tyrosine: Biosynthesis & Melanin Synthesis Promotion

L-Alanyl-L-Tyrosine is a dipeptide formed by the peptide bond linkage of L-alanine and L-tyrosine. Its significant advantage lies in its substantially higher solubility compared to free tyrosine, thereby resolving the issue of poor solubility encountered with tyrosine in parenteral nutrition formulations. This dipeptide undergoes rapid hydrolysis by peptidases in vivo, releasing alanine and tyrosine for utilisation by the body, making it a crucial tyrosine supplement in clinical parenteral nutrition. At the metabolic level, it rapidly labels tissue tyrosine pools, participates in protein synthesis, and exhibits low urinary loss rates. Furthermore, L-Alanyl-L-Tyrosine serves as a bioactive dipeptide for metabolic research, peptide drug synthesis, and enzyme catalytic substrates, finding extensive applications across pharmaceutical, nutritional, and biochemical fields.

L-Alanyl-L-tyrosine in Promoting Melanin Synthesis

As a conditionally essential amino acid in the human body, L-tyrosine is the precursor for the synthesis of the catecholamine neurotransmitters dopamine, epinephrine, and norepinephrine. It is not only used as the raw material for amino acid infusion and amino acid compound preparations, but also for patients with vitiligo to take drugs containing tyrosine to relieve the symptoms of vitiligo. At present, the synthesis method of L-Alanyl-L-Tyrosine is limited to the chemical synthesis method, but this method still has many defects, such as many reagents and complicated reaction steps, and the reaction cost is too high. In addition, the product obtained from the reaction is easy to be racemized and has many side reactions, and the use of toxic organic reagents will also cause potential harm to the human body. The biological enzyme method has been widely concerned by scientists because of its mild reaction conditions, low cost, and high safety to the body. L-Alanyl-L-Tyrosine is a good water-soluble and stable dipeptide; it can quickly decompose and release tyrosine after entering the body. Therefore, it can play a role instead of tyrosine. In this study, alanine methyl ester hydrochloride was used as an acyl donor, disodium tyrosine was used as a nucleophilic reagent, and α-amino acid ester acyltransferase was used to catalyze the synthesis of L-Ala-Tyr in DES system. The synthesis process is shown. On this basis, the optimum reaction conditions for the synthesis of L-Alanyl-L-Tyrosine were studied, and the biological activity of the product was investigated after characterization.[1]

At present, the only known method for the synthesis of L-Alanyl-L-Tyrosine is chemical synthesis. The dipeptide with the protective group is generated by the reaction of L-tyrosine and alanine protected by benzyl chloroformate, and then, the L-Ala-Tyr is obtained by alkaline hydrolysis and hydrogenation to remove the protective group. The yield of the dipeptide synthesized by this method is 77%, and the purity is 99%. In 2004, it was found that α-amino acid ester acyltransferase has extensive substrate specificity for both acyl donors and nucleophilic reagents. It can synthesize a variety of dipeptides, including L-Alanyl-L-Tyrosine, but no quantitative analysis was carried out. Therefore, little information was known about the synthesis of L-Ala-Tyr. In this study, the biosynthesis process of L-Ala-Tyr was reported for the first time. α-Amino acid ester acyltransferase showed great potential for high-yield L-Alanyl-L-Tyrosine dipeptide biosynthesis in a novel DES green reaction medium under optimized conditions (boric acid-borax (0.2 mol/L), 30°C, pH 9.5, the bacterial concentration was 16 U/mmol, acyl donor/nucleophile = 2:1, choline chloride/urea = 1:2, DES water content 15% (v/v)) to achieve a conversion rate of 50%.

This is the highest conversion rate of L-Ala-Tyr synthesized by biosynthesis reported so far, and the conversion rate still needs to be further improved by means of molecular modification. In addition, the preliminary physiological activity identification results show that L-Alanyl-L-Tyrosine has no toxic effect on cells in the concentration range of 100–800 μmol·L−1 and at the optimal concentration, compared with the positive control 8-methoxypsoralen. It can promote the production of melanin. However, the current researches mostly focus on L-tyrosine to prove its biological activity. In cultured hamster melanoma lines, supplementation of L-tyrosine from 10 to 600 μmol·L−1 stimulated not only melanin synthesis but also tyrosinase activity in a dose- and time-dependent manner with kinetics defined by the original melanogenic potential of the cell line. The biological activity of L-Alanyl-L-Tyrosine is used to increase BP in hypotensive rats and decrease BP in hypertensive rats.

References

[1]Fan, Yuna et al. “Biosynthesis, Characterization, and Bioactivity of L-Alanyl-L-tyrosine in Promoting Melanin Synthesis.” Applied biochemistry and biotechnology vol. 196,7 (2024): 3693-3707. doi:10.1007/s12010-023-04713-5

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