Effect of an abundant human skin melanosomal 66 kDa protein (MP 66) on m urine tyrosinase: Its physiological implications on melanogenesis

Milk Protein-Derived Antioxidant Tetrapeptides as Potential Hypopigmenting Agents

Excessive accumulation of melanin can cause skin pigmentation disorders, which may be accompanied by significant psychological stress. Although many natural and synthetic products have been developed for the regulation of melanogenesis biochemistry, the management of unwanted skin pigmentation remains challenging. Herein, we investigated the potential hypopigmenting properties of peptide sequences that originated from milk proteins such as ĸ-casein and β-lactoglobulin. These proteins are known to inhibit melanogenesis and their hydrolysates are reported as antioxidant peptides. We synthesize tetrapeptide fragments of the milk protein hydrolysates and investigate the amino acids that are essential for designing peptides with tyrosinase inhibitory and antioxidant activities. We found that the peptide methionine-histidine-isoleucine-arginine amide sufficiently inhibits mushroom tyrosinase activity, shows potent antioxidant activity and effectively impedes melanogenesis in cultured melanocytes via cooperative biological activities. Our findings demonstrate the potential utility of the bioactive tetrapeptide from milk proteins as a chemical alternative to hypopigmenting agents.

Partial characterization of an abundant human skin melanosomal 66 kDa protein (MP 66) and investigation to purify a similar protein from B16 murine melanoma tumours

A single polypeptide protein of molecular weight 66kDa (MP 66), purified to homogeneity from melanosomes of normal human cadaver skin epidermal melanocytes, was further characterized. Based on the yield in the present investigation, the intracellular concentration of this protein was calculated to be 4.2 microM. It was shown to be a glycoprotein on gel electrophoresis. Based on its partial N-terminal amino acid sequence, it was shown to be distinct from known melanosomal proteins such as gp 75, tyrosinase-related protein-2 (TRP-2) and Pmel 17. Investigation to purify a similar type of protein from B16 murine melanoma tumours by following the same purification procedure resulted in a partially purified protein with a molecular weight of 66 kDa. However, unlike MP 66, this protein did not show inhibition of the monophenolase activity of tyrosinase at pH 6.8. Finally, the effects of 0.5 mM each of CaCl2, ZnSO4 and FeSO4 together, and of human skin epidermal melanosomal proteins, were studied on melanin polymerization at pH 4.7. The metal cations failed to initiate melanin polymerization, while melanosomal proteins did in a dose-dependent manner.