6.
DI0CUS�.)ION
6.1
7 5 -
The d a t a on th e s edimentation char�c t eris t i c s o f th e ·purified em�yme i nd i c a t ed that, a t pH 8 , s h e e p h e art J:lFK exi s t s as a polymer in rapid rever s ib l e equilibrium with l ower MW form s . '11he schliercn pattern c ont ained tv1o p e al�s a.t 7 and 30 S and
a m inor shoulder at 1 9 G ; this d i f f ers from the s j_ tua t i on
,,,i th rabb i t muscle FFK , where the 30 S boundary contains prominent shoulders at 1 9 and 1 2 S ( Ling et al . , 1 965 ; Enm e�giani et al . ,
1 966 ;
Paetkau a nd Lardy, 1 967 ; Uyeda , 1969) . The differenc e in shape o f th e trailing 30 Sb oundary p a s s ibly re f l ec t s a di fference in the equilibrium
c on s t ant f o r the p o lym eri s at i o n re ac ti on b e t w e en th e two
s ourc es o f enzyme . She ep heart PFK undergoes a concentration
dependent polymerisation. The c o nc entrati on dependenc e of
the s edimentat ion rat e o f the 30 S bom)dary obs erved here is
virtua l ly i dentic a l to that reported for rabb i t mus c l e
( Leonard and Walker , 1 97 2 ) . Thi s would indi c a t e that the po lymer of the equi l ibrium r e action has the s a�e molecular
w e i gh t in b o th spec i e s . The ma j or difference in the s edi mentation pattern b e tween the t wo en zymes i s the ab s enc e of
7 S materia l in rabb i t mu s c l e at pH 8 . This form of the enz yme do e s , however , exi B t i n equi l ibrium wi th th e 1 2 S form o f rabb it mus c l e , at pH value s betwe en 6 and 8 ( Aaron s on and
� Frieden, 1 972) .
In contrast to the purified enzyme, the disso lved crystalline
enzyme , s ediment e d as a s ingl e trailing 30 S boundary wi th no
7 S mat e r i a l ( a s imilar r e s ul t has b e en rec ent ly r eport e d for
the enzyme from chicken l iver ( Kono et al . ,
1 973 ) ) .
From this ,i t would app ear that the 7 S s p ecies do es not r e pr e s ent the monomer in the forma t i on of th e 30 S s p ec i es o f s h e ep heart . Wh en th e s ediment at i on patt ern of the di s s olved crys t a l l ine en zyme was r e inve s t i ga t e d aft er s even days , th e r e was no c hange in the pattern ; this is s i gnific ant in tha t it a l s o sum:;e s ts that the 7 S form i s not i n equi librium w i th the 3 0
S
speci es. By anal ogy with rabbit mus c l e , i t appears likely tha t the monom er o f polym er i s a t i on o f she ep heart
PFK , at
76 .