From hydrolysis experiments carried out on αs1-caseins
A and F at pH 5·2
in the presence of 30 g NaCl/l, i.e. the conditions encountered in
many young goats'
cheeses, it was found that minima of 19 and 9 bonds were sensitive to chymosin
in
variants A and F respectively. Variant A was hydrolysed faster than variant
F and
the proteolytic pattern (reversed-phase HPLC and polyacrylamide agarose
gel
electrophoresis) differed between the variants. Hydrolysates from both
variants had
a number of cleavage sites in common (Leu20–Leu21,
Phe23–Ala24 and Phe32–Arg33
in
both variants, Leu101–Lys102 and
Leu64–Lys65, Leu120–His121
and Leu83–His84, Leu142–Ala143
and Leu105–Ala106, Leu149–Phe150
and Leu112–Phe113, Leu156–Asp157
and Leu119–Asp120, Trp164–Tyr165
and Trp127–Tyr128 in variants A and F respectively),
while other bonds were split only in variant A (Leu16–Asn17,
Glu18–Asn19, Phe28–Pro29,
Ile44–Gly45, Tyr80–Ile81,
Gln82–Lys83, Tyr91–Leu92,
Tyr94–Leu95, Leu109–Glu110
and
Phe179–Ser180). Major cleavage sites appeared
to be at
Phe23–Val24, Leu142–Ala143
and
Trp164–Tyr165 for variant A, and
Phe23–Val24 and Leu64–Lys65
for variant F. Cleavage site Phe23–Val24
could be the origin of the first breakdown product from goat
αs1-caseins A and F visible in polyacrylamide agarose
gel electrophoresis.