beta-Keratins: Keratins that form into a beta-pleated sheet structure. They are principle constituents of the corneous material of the carapace and plastron of turtles, the epidermis of snakes and the feathers of birds.Reptilian Proteins: Proteins obtained from species of REPTILES.Colubridae: The largest family of snakes, comprising five subfamilies: Colubrinae, Natricinae, Homalopsinae, Lycodontinae, and Xenodontinae. They show a great diversity of eating habits, some eating almost anything, others having a specialized diet. They can be oviparous, ovoviviparous, or viviparous. The majority of North American snakes are colubrines. Among the colubrids are king snakes, water moccasins, water snakes, and garter snakes. Some genera are poisonous. (Goin, Goin, and Zug, Introduction to Herpetology, 3d ed, pp321-29)Alligators and Crocodiles: Large, long-tailed reptiles, including caimans, of the order Loricata.Epidermis: The external, nonvascular layer of the skin. It is made up, from within outward, of five layers of EPITHELIUM: (1) basal layer (stratum basale epidermidis); (2) spinous layer (stratum spinosum epidermidis); (3) granular layer (stratum granulosum epidermidis); (4) clear layer (stratum lucidum epidermidis); and (5) horny layer (stratum corneum epidermidis).Proline: A non-essential amino acid that is synthesized from GLUTAMIC ACID. It is an essential component of COLLAGEN and is important for proper functioning of joints and tendons.Birds: Warm-blooded VERTEBRATES possessing FEATHERS and belonging to the class Aves.