alpha(s1)-, alpha(s2)-, beta- and kappa-caseins from Somali camels (Ca
melus dromedarius) were purified by acid precipitation at pH 4.4, crud
ely separated into an alpha-CN and a beta-CN fraction and further puri
fied by reversed-phase HPLC. Fragments of tryptic digests were sequenc
ed. Amino acid patterns obtained were used to screen a cDNA library co
nstructed from mRNA from lactating udder tissue. Pull length clones co
rresponding to the four caseins were sequenced. The numbers of residue
s in the sequences deduced were alpha(s1)-CN 207, alpha(s2)-CN 178, be
ta-CN 217, kappa-CN 162. Percentage similarity to bovine proteins was
alpha(s1)-CN A 39, a(s2)-CN 56, beta-CN 64, kappa-CN 56. Acid-precipit
ated casein of pooled milk was separated by reversed-phase HPLC and mo
nitored at 220 nm, and its composition, estimated from peak integratio
n, was (g/kg total casein) alpha(s1)-CN 220, alpha(s2)-CN 95, beta-CN
650, kappa-CN 35. Degrees of phosphorylation and glycosylation were de
termined by laser ionization mass spectrometry and sequence pattern an
alysis. Molecular masses dieter mined were (kDa) a(s1)-CN A, 24.755 an
d 24.688; alpha(s1)-CN B, 25.293; a(s2)-CN 21.993; beta-CN, 24.900; ka
ppa-CN 22.294-22.987. The pH values of the most probable isoelectric p
oints were: alpha(s1)-CN A 6P 4.41, alpha(s1)-CN B 6P 4.40, alpha(s2)-
CN 9P 4.58, beta-CN 4P 4.66, kappa-CN 1P, with tensialic acid residues
bound. 4.10.