MILK PROTEINS 1611 28/29 1051 107/ 209
106 108
PP8 fast
(P-CN f 1-28) .I'-(WN f 29-209)PP8 slow (HN f 29-105/7) ?CWN f 108-209)- b
PP-5 (HN f 1-105/7)
- Figure 4.7 Principal products produced from p-casein by plasmin.
Table 4.3 Old and revised nomenclature for y-caseins
Recommended
nomenclature
Old Trivial @-casein sequence)7
TS-A' ;.LA2 b-CN A', (f106-209)
S ?2-B j-CN B, (f106-209)
R ?3-A j-CN A2, (f108-209)
TS-B ;J3-B j-CN B (f108-209)?-A', yl-A2, yL-A3, 7'-B P-CN A', A2, A3, B (f29-209)A and B indicate genetic variants, see p. 162.prepared by chromatography on DEAE-cellulose since they do not adsorb
even at low ionic strength (0.02 M) at pH 6.5; $-casein adsorbs at pH 8.5
but y2- and "/-caseins do not.
Isolated %,,-casein in solution is also very susceptible to plasmin; eight
peptide bonds are hydrolysed with the production of 14 peptides. Plasmin
also hydrolyses r,,-casein in milk but the peptides formed have not been
identified, although at least some are included in the proteose-peptone
fraction.
Although less susceptible than p- and &,,-caseins, isolated %,,-casein in
solution is also readily hydrolysed by plasmin. It has been suggested that a
minor ill-defined fraction of casein, called ,&casein, consists of plasmin-
produced fragments of &,,-casein, but the situation is unclear.
Variations in the degree of glycosylation. ic-Casein is the only one of the
principal milk proteins which is normally glycosylated but, as discussed on