H. Glover et Cj. Brady, PECTINESTERASES FROM MATURE, UNRIPE PEACH FRUIT BIND STRONGLY TO PECTIC POLYSACCHARIDES, Australian journal of plant physiology, 22(6), 1995, pp. 977-985
Contrary to previous findings, the level of the pectin de-esterifying
enzyme, pectinesterase (PE; EC 3.1.1.11), is shown to be much higher i
n mature, green peach fruit than in ripe fruit. Aqueous buffers readil
y extracted three pectinesterase isoforms from ripe fruit but only a p
ortion of the activity from mature, green fruit. In mature, green frui
t extracts the enzyme precipitated when the ionic strength was lowered
; consequently isoforms could not be recovered by ion exchange chromat
ography. In extraction residues from mature, green fruit, residual PE
could be measured as active enzyme and, when denatured, could be detec
ted by immunological techniques. Extraction of the enzyme was enhanced
after digestion of the tissue with pectin lyase. The extracted enzyme
fractionated as a large molecular weight complex rich in uronic acid,
rhamnose, galactose and arabinose. After further digestion with endo-
beta-1,4-galactanase, the enzyme was in two fractions of smaller size
but with residual carbohydrate. When mature, green and ripe fruit tiss
ue were co-extracted, the recovered activity was as predicted from ind
ependently extracted tissues demonstrating that enzyme activity was no
t influenced by inhibitors contributed by either tissue type. Isoforms
known to be present in the ripe fruit were recovered from extracts of
the mixed tissues. It is concluded that PE in extracts of mature, gre
en fruit has a strong association with pectic polymers and this has le
ad to its underestimation in previous studies. It is suggested that su
ch an association with pectin polymers in vivo may regulate enzyme act
ivity and enzyme turnover.