The Relative Rates of Destruction of Pectin in Macerates of Various Citrus Fruits.

نویسندگان

  • M A Joslyn
  • A Sedky
چکیده

The natural pectins are believed to consist of long, open, unbranched chains of galacturonic acid with an occasional arabinose and galactose molecule. The free carboxyl groups of the galacturonic acid are partially or wholly esterified with methyl alcohol, and an occasional hydroxyl group is esterified with acetic acid [BONNER (4), BRANFOOT (5), FREUDENBERG (7), GADDUM (8), KERTESZ (13), MYERS and BAKER (16), NORMAN (18, 19), RIPA (22) ]. The differences found among the natural pectins are believed to arise from differences in the extent of esterification, and in the extent of polymerization. The view that pectinis originate phytochemically by the progressive oxidation of the sixth carbon atoms of the galactose residues occurring in galactans, followed by decarboxylation has been recently questioned by the finding of HIRST and JONES (10) that the araban found in close association with the pectic acid of the peanut is composed entirely of the arabofuranose residues instead of the expected arabopyranose residues. On the assumption that the pectin molecule consists of galacturonic acid, galactose, arabinose, acetyl, and methoxyl units the pectic enzymes should number at least seven specific enzymes acting uponi the possible linkages between these units. In addition we would expect the presence of enzymes of initial attack differentiated by their abilitv to attack pectins of different degrees of polymerization. Accepting "protopectinase " as such an enzyme, there are at present known but four specific enzymes (13) of which pectin methoxylase has been most widely stuLdied. The complexity of the pectins, the diversity of the enzymes acting upon them and the difficulty of obtaining either puLre pectic enzymes or substrates of definite constitution and configuration have complicated this field. It has been only recently that systematic studies on fairly well defined substrates were begun by EHRLICH (6) and independently by KERTESZ (13). The separation of the various componients of the pectinase complex, their purification anid investigation is yet to be undertaken. ROTHSCHILD (23) pointed out in this connection the possibility of separating "pectolase" from "pectase" by making use of the different rates at which these are destroyed in acid and alkaline soluLtions. 1 Presented at the 23rd annual meeting of the Pacific Divisioni, A.A.A.S., Staniford University, June 29, 1939.

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عنوان ژورنال:
  • Plant physiology

دوره 15 4  شماره 

صفحات  -

تاریخ انتشار 1940