Vitamin C in Walnuts

Pyke, Magnus; Melville, R.; Sarson, H. S.

doi:10.1038/150267b0

Cited by 6 publications

(4 citation statements)

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“…Subsequently, there was a gradual loss of vitamin C up to maturity. HENNIG and OHSKE (2) confirmed these observations and noted that the percentage of total vitamin C (ascorbic and dehydroascorbic acid) in the green hulls decreased from 1.0% in July to 0.26%o in October; the dehydro-form represented less than one-tenth of the total vitamin C. A maximum value of 1.8%o ascorbic acid in the whole immature walnuts was reported by PYKE, MELvILLE, and SAR-SON (3). MELVLLE, WOKES, and ORGAN (4) measured the amount of reductones1 in immature walnuts ranging in weight from 2 to 40 grams, and found about 30%o of the total apparent (dichlorophenol-indophenol titratable) vitamin C to be reductones.…”

supporting

confidence: 71%

Vitamin C Content of Walnuts (Persian) During Growth and Development

Klose¹,

Peat²,

Fevold³

1948

Plant Physiol.

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The remarkably high concentration of vitamin C in immature walnuts and in walnut hulls was first reported by GHERGHELEZHIU (1), who noted that the walnuts developed a maximum concentration of 2.5% vitamin C (wet basis) just before hardening of the shell took place. Subsequently, there was a gradual loss of vitamin C up to maturity. HENNIG and OHSKE (2) confirmed these observations and noted that the percentage of total vitamin C (ascorbic and dehydroascorbic acid) in the green hulls decreased from 1.0% in July to 0.26%o in October; the dehydro-form represented less than one-tenth of the total vitamin C. A maximum value of 1.8%o ascorbic acid in the whole immature walnuts was reported by PYKE, MELvILLE, and SAR-SON (3). MELVLLE, WOKES, and ORGAN (4) measured the amount of reductones1 in immature walnuts ranging in weight from 2 to 40 grams, and found about 30%o of the total apparent (dichlorophenol-indophenol titratable) vitamin C to be reductones. However, LUOG and WELL.ER (5) reported that only 5-107o of the total reducing capacity of the walnut extracts could be assigned to reductones, and that only about 5% of the total vitamin C (ascorbic plus dehydroascorbic acid) occurred as dehydro-acid. Recently TUBA, HUNTER, and OSBORNE (6), using the method of LEVY (7), have published values for the non-vitamin C reductants, expressed as percentage of total indophenol dye reductants, of 38%o for the whole immature walnut of 4.2 gm. weight, and 24%o for a walnut weighing 8.5 gm.As a part of investigations dealing with the utilization of waste walnut hulls as a commercial source of vitamin C, we have measured the vitamin C content of the Persian (English) walnut at different stages of development during two seasons. The amount of reductones and the distribution of vitamin C in the differentiated structures of the maturing walnut have also been determined. The amount of biologically active vitamin C in the immature walnuts has been measured and compared with the values obtained by the chemical methods. ProcedureThe data presented in this paper were obtained from experiments with walnuts of five commercial varieties, grown in Ignacio Valley near Walnut Creek, California. Walnuts were picked from the trees and immediately 1 The term " reductones " as used in this report refers to the naturally occurring and derived substances which give the reduction of 2.6 dichlorphenol indophenol dye characteristic of vitamin C but have no vitamin C activity. 133www.plantphysiol.org on May 9, 2018 -Published by Downloaded from

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supporting

confidence: 71%

Vitamin C Content of Walnuts (Persian) During Growth and Development

Klose¹,

Peat²,

Fevold³

1948

Plant Physiol.

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“…This is much higher than the approximately 30 pM found in blood plasma 1371. Studies by immuno-histochemistry and in situ hybridization have, however, shown that the expression of uPA in tissue-remodeling events is often highly localized to specific areas, such as the migrating keratinocytes at wound edges [38,391 and the interface between cancer cells and stromal cells at invasive foci in tumors 140-421. uPAR is expressed in the same areas, often being produced by different cell types, indicating a cellular interplay in regulation of plasminogen activation [42,431. These findings point to large differences in the local concentration of uPA and suggest that high concentrations occur in areas where the physiological interaction with uPAR takes place.…”

Section: Discussionmentioning

confidence: 99%

Cell‐Surface Acceleration of Urokinase‐Catalyzed Receptor Cleavage

Høyer‐Hansen

Ploug

Behrendt

et al. 1997

European Journal of Biochemistry

106

127

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The urokinase-type plasminogen activator (uPA) binds to a specific cell-surface receptor, uPAR. On several cell types uPAR is present both in the full-length form and a cleaved form, uPAR(2+3), which is devoid of binding activity. The formation of uPAR(2+3) on cultured U937 cells is either directly or indirectly mediated by uPA itself. In a soluble system, uPA can cleave purified uPAR, but the low efficiency of this reaction has raised doubts as to whether uPA is directly responsible for uPAR cleavage on the cells. We now report that uPA-catalyzed cleavage of uPAR on the cell surface is strongly favored relative to the reaction in solution. The time course of uPA-catalyzed cleavage of cell-bound uPAR was studied using U937 cells stimulated with phorbol 12-myristate 13-acetate. Only 30 min was required for 10 nM uPA to cleave 50% of the cell-bound uPAR. This uPA-catalyzed cleavage reaction was inhibited by a prior incubation of the cells with uPA inactivated by diisopropyl fluorophosphate, demonstrating a requirement for specific receptor binding of the active uPA to obtain the high-efficiency cleavage of cellbound uPAR. Furthermore, amino-terminal sequence analysis revealed that uPAR(2 + 3), purified from U937 cell lysates, had the same amino termini as uPAR(2+3), generated by uPA in a purified system. In both cases cleavage had occusred at two positions in the hinge region connecting domain 1 and 2, between Arg83-Ah84 and Arg89-Ser90, respectively. The uPA-catalyzed cleavage of uPAR is a new negativefeedback regulation mechanism for cell-surface plasminogen activation. We propose that this mechanism plays a physiological role at specific sites with high local concentrations of uPA, thus adding another step to the complex regulation of this cascade reaction.

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“…The remarkably high concentration of vitamin C in unripe walnuts (Juglan8 regia) appears to'have been first reported by Gerghelezhiu (1937), and has been confirmed by Pyke, Melville & Sarson (1942) who also examined a number of allied species and genera. Melville, showed that unripe walnuts and nuts from allied species may also contain considerable amounts of apparent vitamin C, the provisional term suggested by Wokes, Organ, Duncan & Jacoby (1943) to describe substances occurring in certain foods, and, although not possessing the antiscorbutic potency of vitamin C, not distinguished from it by the indophenol dye titration as usually carried out.…”

mentioning

confidence: 55%