Ferrocarril y su incidencia sobre el territorio

et al . , 1 964 ; l'1ackinlay and �.fake , 1 964 ; Talb o t and \.J'augh ,

1 970 ) .

Alkaiine gel elec trophoresis in the pres enc e of urea of r e duc ed K -c as ein c ontaining a s ingl e genetic variant rev e al ed one int ens ely s taining band and approximat ely five minor bands v11ith great er mobility ( I'1ackinlay and 1tlake , 1 964 ; Schmidt , 1 964 ; Woychik , 1 964 ) . Thes e rapidly migrating bands , which only acc ount for a proportion of K-cas ein , diff er from the slower , more int ens e band in their c arbohy­ drat e c ont ent ( \Joychik , et al . , 1 966 ; Mackinlay and ·wake , 1 96 5 ; Schmidt et al . , 1 966 ) . The maj or c omponent c ontains no c arbohydrat e , whi l e the minor b ands pos s es s increas ing

amounts o f h exo s e and s i alic ac i d . Treatment of thes e c as eins with neuraminadas e reduc es the int ens ity o f thes e minor c omponents , c ons istent with the removal of s ialic acid

from the l eading bands ( Schmidt et al . , 1 966 ) . Thes e bands � l s o dis appear on treatment with rennet ( Ros e et al . , 1 970 ; Schmidt et al . , 1 966 ) . The l ack of c arbohydrat e does not

aff ect the mic el l e stabilizing ability of K-c as ein ( Mackinlay and Wake , 1 965) .

Ribadeau Dumas et al . ( 1 964 ) purifi ed "-cas ein by chromat ography o f whol e c as ein on DEAE-c ellul o s e in buffer c ont aining ur e a . Lat er , K-c as ein was is o lat ed by chromato­ graphy on DEAE-c ellul o s e aft er the disulphide groups were reduc ed ( Schllildt e t a l . , 1 966 ; I'1ackinlay and Vake , 1 965 ; Iuj o l l e et a l . , 1 966 ; Woychik et al . , 1 966 ) .

b � I

Rec ently , Yaguchi and T aras suk ( 1 967 ) and Yaguchi et

al . ( 1 968 ) describ ed a proc edure for the is olation of

«�c as ein from milk or cas ein by chromatography on Sephadex G-1 50 in th e pres enc e of 6 I-1 urea . 0inc e ,:-c as ein is int er­ mol ecularly linked through its disulphide b onds , in the

abs enc e of 2-mercapt o ethanol it i s elut ed as a peak at the

void volume of the c o lumn . The s e proc edures for iso l at ing

�e -c as eins , uti l i z ing chromatography on ·DEAE-c ellulos e and S ephadex G-1 50 and the proc edure described by l'TcKenz i e and �ake ( 1 961 ) , do not expos e the prot eins to the rigorous c onditions experi enc ed using the urea-sulphuric ac id

frac tionation method of Zit t l e and Cus t er ( 1 963 ) . Other methods us ed to i solate �e -c a s ein are describ ed in the revi ew by Mackinlay and Wake ( 1 971 ) .

6 . 5 of K -e as ein

63 I

"-cas ein is s o lubl e in s o lutions c ontaining moderat e l evels of e a "V-li th 2 e; atoms b e ing bound to the prot ein

( Dicks on and Perkins , 1 971 ) . However , s inc e only 1 phosphat e group is pr es ent in K-cas ein ( I-1erc i er et al . , 1 973 ) , an

additional binding s i t e for ea may exist .

J

WauGh and hi s c oworkers have large ly b e en resp onsib l e for the work

by K-c as ein . mic e l l e-typ e

on the s tab ilization in solution of as1 .-cas ein �1 -eas ein and K-cas ein can form s o lub l e

c ompl exes i n the pr es en� e o f e a ( s tabilizat i on ) , under c ondi t i ons where as 1 -cas ein would normally prec ipitat e . Although they ori ginal ly beli eved complexes b e tween K-c as e in and a81 -cas e in formed s pontaneous ly , with a pr eferred weight rat i o a _s 1 -c as e in : K -cas ein of 4 in the abs enc e o f e a

0

( waugh , 1 958 ) , rec ent r e sult s s ugg ested the c ompl ex at 37 e wm c ompos ed of a unit weight rat i o o f the two prot eins

( Waugh and Nobl e , 1 96 5 ; Noble and Haugh , 1 965 ) . This work l ed to a study of mic e l l e format i on with as 1 - and K -cas ein in the pres enc e and abs enc e of e a . For a des cript i on o f thi s work the reader is r e f err ed to the recent r evi ew by Waugh

( 1 971 ) .

6 . 6 - Ac t i on o f Rennin on K-e as ein

Addition of r enn et to normal milk at room t emp �rature r es ults in rapid c lotting . This is the result of an

extr emely lab i l e ph enylalanine-methi onine peptide b ond b eing c l e aved ( Fi g . 6 . 2 ) , c aus ing a los s of the s t ab i l i z ing ab il ity of K-c as ein , and the generat i on o f para- « - c as e in and mac ro­ peptide ( J olles et al . , 1 963 ; D e lfour et al . , 1 965 ; Jolles , 1 966 ; Jolles et al . , 1 968 ) . The macropeptide has an

N-t errninal m ethionine ( Delfour et al . , 1 96 5 ) and a c ommon e-t erminal s eq uenc e to K-cas ein ( Jolles , 1 966 ) . The sub-

s t itution s it e s respons ibl e for the· A and B _{genet ic variants} o f K-c as e in exis t in the macropeptide ( de Koning et al . , 1 966 ; Woychik et al . , 1 966 ) , as well as the s ingl e phos phoryl at ed res i due ( Fi g . 6 . 2 ) � The macropeptide is also the site of attachment for the c arb ohydrat e r es idues ( Mackinlay and Wak e , 1 965 ; Mackinlay et a l . , 1 966 ; Fiat et al . , 1 972 ) . The