Melanocyte stimulating hormone and melanin concentration hormone may be structurally and evolutionarily related.
Two melanotropic peptides, melanin concentration hormone (MCH) and alpha-melanocyte stimulating hormone (alpha-MSH), exert opposing actions on melanosome (melanin granule) movements within teleost pigment cells, melanocytes (melanophores). MCH stimulates melanosome aggregation to the cell center whereas alpha-MSH stimulates pigment organelle dispersion out into the dendritic processes of the melanocytes. The actions of alpha-MSH are dependent upon extracellular calcium (Ca2+), whereas those of MCH are actually enhanced in the absence of the cation. At high concentrations (10(-5)-10(-8) M) MCH also exhibits MSH-like activity (autoantagonism), an effect which is abolished in the absence of Ca2+. Therefore, MCH exhibits MCH-like as well as MSH-like activity depending on the presence or absence of extracellular Ca2+. An analogue of MCH, [Ala5, Cys10]MCH, has been synthesized which is totally devoid of MCH activity but still exhibits MSH-like activity. These results suggest that the two melanotropic peptides share some component of structural similarity and may be evolutionarily related.
Castrucci
A M
AM
Departamento de Fisiologia Geral, Universidade de São Paulo, Brazil.
Hadley
M E
ME
Lebl
M
M
Zechel
C
C
Hruby
V J
VJ
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D002118:Calcium / Q000502:physiology; D005399:Fishes; D007028:Hypothalamic Hormones; D008543:Melanins / Q000235:genetics*; D008544:Melanocytes / Q000502:physiology; D008969:Molecular Sequence Data; D010907:Pituitary Hormones / Q000235:genetics*; D000521:alpha-MSH / Q000235:genetics*
D007028:Hypothalamic Hormones; D008543:Melanins; D010907:Pituitary Hormones; D000521:alpha-MSH; C019463:melanin-concentrating hormone; D002118:Calcium