Comparisons of the structural and chemical properties of melanosomes isolated from retinal pigment epithelium, iris and choroid of newborn and mature bovine eyes.
Melanosomes were isolated from the retinal pigment epithelium (RPE), iris and choroid of mature (age >2 years) and newborn (age <1 week) bovine eyes. Scanning electron microscopy was utilized to analyze the morphology of the melanosomes, which were found to vary among different tissues and different ages. While the total content of amino acids differs slightly (ranging from 9% to 15% by mass), the distributions of the amino acids are similar. The pheomelanin content is low in the choroid and the RPE (0.1-0.5%), and moderate in the iris (<2%); therefore, the major melanin component of bovine eye melanosomes is eumelanin, independent of the shape of the melanosomes. The yields of pyrrole-2,3,5-tricarboxylic acid from melanosomes decrease in the following order: choroid > iris > RPE, and exhibit decreasing yields with age. 13C solid-state nuclear magnetic resonance (NMR) spectroscopic analysis of iris and choroid melanosomes indicates the same trends. These observations suggest that the 5,6-dihydroxyindole-2-carboxylic acid contents decrease in the following order: choroid > iris > RPE, and decrease with age. Moreover, the 13C solid-state NMR spectra show (1) for the same age samples, the CH:Cq ratio for choroid is larger than that for iris melanosomes; and (2) an increase in the concentration of carbonyl groups with age within each type of melanosome.
Liu
Yan
Y
Department of Chemistry, Duke University, Durham, NC 27708-0346, USA.
Hong
Lian
L
Wakamatsu
Kazumasa
K
Ito
Shosuke
S
Adhyaru
Bhavin B
BB
Cheng
Chi-Yuan
CY
Bowers
Clifford R
CR
Simon
John D
JD
D000328:Adult; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D002829:Choroid / Q000737:chemistry* / Q000648:ultrastructure; D005123:Eye / Q000737:chemistry* / Q000648:ultrastructure; D006801:Humans; D007211:Indoles / Q000032:analysis; D007231:Infant, Newborn; D007498:Iris / Q000737:chemistry* / Q000648:ultrastructure; D008543:Melanins / Q000032:analysis; D020460:Melanosomes / Q000737:chemistry* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning / Q000379:methods; D010857:Pigment Epithelium of Eye / Q000737:chemistry* / Q000648:ultrastructure; D011758:Pyrroles / Q000032:analysis
D000596:Amino Acids; D007211:Indoles; D008543:Melanins; D011758:Pyrroles; C018362:pheomelanin; C041877:eumelanin; C030692:5,6-dihydroxy-2-indolylcarboxylic acid; C071226:pyrrole-2,3,5-tricarboxylic acid