Protein content of molar-incisor hypomineralisation enamel.
OBJECTIVE
The aim of the study was to compare the relative amounts and nature of the proteinous content of sound and molar-incisor hypomineralisation (MIH) enamel.


METHODS
TCA (20%) was used to dissolve the mineral phase and precipitate the proteins from enamel pieces sectioned from sound and MIH enamel. The protein content was estimated using a miniaturized version of the method of Lowry et al. Samples of the solubilised protein were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), stained with Coomassie Blue R250 and tryptic fingerprint/mass spectrometry (MS/MS) of bands in excised gel pieces used for protein identification.


RESULTS
Compared to sound enamel, brown enamel showed a 15-21-fold higher protein content, and yellow and chalky enamel showed about 8-fold higher protein content. Tryptic fingerprint/MS performed on excised 50-70kDa areas demonstrated serum albumin, type I collagen and antitrypsin to be common to all types of enamel. Yellow and brown enamel showed more abundant serum albumin and antitrypsin, and the presence of serum antithrombin. Albumin is reported to be an inhibitor of crystal growth, and antitrypsin and antithrombin inhibit kallikrein 4 proteolytic activity.


CONCLUSIONS
The combination of the effects of serum proteins on developing enamel may result in elevated proteinous content and reduced mineral content as seen in MIH enamel.
Farah
Rami A
RA
Department of Oral Sciences, Faculty of Dentistry, University of Otago, Great King Street, Dunedin, New Zealand. rami.farah@otago.ac.nz
Monk
Brian C
BC
Swain
Michael V
MV
Drummond
Bernadette K
BK
D000990:Antithrombin III / Q000032:analysis; D007611:Aprotinin / Q000032:analysis; D002648:Child; D024042:Collagen Type I / Q000032:analysis; D000090602:Collagen Type I, alpha 1 Chain; D003743:Dental Enamel / Q000737:chemistry* / Q000473:pathology; D003744:Dental Enamel Hypoplasia / Q000378:metabolism* / Q000473:pathology; D003746:Dental Enamel Proteins / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007202:Indicators and Reagents; D007610:Kallikreins / Q000037:antagonists & inhibitors; D012394:Rosaniline Dyes; D012709:Serum Albumin / Q000032:analysis; D053719:Tandem Mass Spectrometry; D014361:Trypsin Inhibitors / Q000032:analysis; D000515:alpha 1-Antitrypsin / Q000032:analysis
C490889:AMBN protein, human; D024042:Collagen Type I; D000090602:Collagen Type I, alpha 1 Chain; D003746:Dental Enamel Proteins; D007202:Indicators and Reagents; D012394:Rosaniline Dyes; C043392:SERPINA1 protein, human; D012709:Serum Albumin; D014361:Trypsin Inhibitors; D000515:alpha 1-Antitrypsin; C048139:Coomassie blue; D000990:Antithrombin III; D007611:Aprotinin; D007610:Kallikreins; C120801:kallikrein 4