An Electron Microscopic Study of the Location of κ-Casein in Casein Micelles by Periodic Acid-Silver Methenamine Staining

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Abstract
The periodic acid-silver methenamine staining method for carbohydrate was applied to ultrathin sections of fixed [bovine milk] casein micelles to determine the location of .kappa.-casein in these particles. Staining for 60 min resulted in the deposition of Ag in uniformly distributed regions throughout all sizes of micelles. A shorter staining procedure (10 min) produced evenly distributed silver grains in small micelles (apparent diameter less than 100 nm) while in large micelles (apparent diameter more than 220 nm) the metal grains were deposited in the outer portions with few in the center regions. This is interpreted as indicating that while .kappa.-casein as a whole is distributed throughout the casein micelle, the more highly glycosylated molecules of the protein are located in the outer portions of the particle.