摘要:

Clostridium perfingenstype A enterotoxin has 8 amino groups which are readily reactive with 2, 4, 6‐trinitrobenzene sulfonic acid (TNBS) in 20 mM phosphate buffer, pH 6.8, and 10 amino groups which react with TNBS only after denaturation with 6.5 M guanidine · HCl ≤ 25°C. The one sulfhydryl group of enterotoxin is not reactive with 5,5′‐dithiobis‐(2‐nitrobenzoic acid) (DTNB) in the native molecule (phosphate buffer, pH 6.8), but is reactive in the presence of 0.2% sodium dodecyl sul

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1980.tb00781.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

The effects of sodium dodecyl sulfate, guanidine · HCl, heat and pH on the tertiary structure of Clostridium perfringens type A enterotoxin were determined by UV difference spectroscopy and by accessibility of the amino groups to 2, 4, 6‐trinitrobenzene sulfonic acid (TNBS) and the one sulfhydryl group to 5, 5′‐dithiobis (2‐nitrobenzoic acid) (DTNB). Biological stability of enterotoxin at several pH's at 55°C in the presence and absence of borate and dipicolinate ions was determined by the guinea pig skin test. Sodium dodecyl sulfate and heat did not unfold the molecule while treatment with>4.5Mguanidine · HCl at ≥25°C completely unfolded the molecule based on UV difference spectral changes and the accessibility of the amino groups to reaction with TNBS. Sodium dodecyl sulfate, at 0.2%, made the sulfhydryl group accessible to DTNB but did not affect the accessibility of the amino groups (7.89 ± 0.15 groups in the native molecule). Guanidine · HCl, at 6.5Mfor 30 min and ≥25°C, made all 17 e‐amino groups and the one α‐amino group accessible to TNBS. At pH's above 8 spectral differences, in relation to the spectrum at pH 6.8, were associated primarily with ionization of the tyrosine residues while at pH's below 5.5 the spectral changes were probably a result of protonation of carboxyl groups in the vicinity of tyrosine and tryptophan resid

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1980.tb00782.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

A purified, homogeneous tomato fruit peroxidase was used to study the oxidation of indoleacetic acid (IAA) in the presence of a phenolic compound and managanese. The reaction was completely inhibited by potassium cyanide and sodium meta‐bisulfite when these compounds were added initially. However, when these compounds were added after the reaction had begun, potassium cyanide did not completely inhibit whereas sodium meta‐bisulfite did. Also, the ultraviolet spectrum of the reaction products indicated that methyleneoxindole was the primary product. Several monophenols were capable of serving as cofactors, but o‐dihydroxyphenols were inhibitors of IAA oxidation by tomato peroxidase. The inhibition was characterized by an extension of the induction period after which oxidation proceeded as normal.These results suggest that IAA oxidation by tomato fruit peroxidase proceeds autocatalytically via a free radical mechanism and that o‐dihy‐droxyphenols could be serving as chain‐stopping agents. The changes in the phenolic pool during fruit development could affect IAA oxidation and be related to the fruit ripen

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1980.tb00783.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

The localization of peroxidase activity a t the ultrastructural level in tomato fruit (Lycopersicon esculentum Mill cv. Walters) has been accomplished using the diaminobenzidine histochemical reaction. In immature tomato fruit the peroxidase activity was most prominent at the inner surface of the tonoplast, although some cell wall activity was observed. However, in mature tomato fruit most of the peroxidase activity was localized in the cell wall. No activity was found in organelles or in the cytoplasm of either immature or mature fruit. The significance of these observations is discussed in relation to the physiological role of the enzyme in fruit ripening.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1980.tb00784.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

The mitochondrial‐associated CTP: phosphatidic acid cytidylyltransferase (CDP‐diacylglycerol synthase, EC 2.7.7.41) was studied from germinating soybeans. The enzyme exhibited a broad pH optimum between pH 6.5 and pH 8.0. Activity was dependent on the addition of magnesium ions (20 mM) and the nonionic detergent Triton X‐100 (5 mM). The apparent Kmvalues for CTP and phosphatidic acid were 0.58 mM and 0.12 mM, respectively. A Vmaxof 0.12 U/mg was found for the mitochondrial‐associated enzyme. Phospholipids generally stimulated activity while ADP and CDP strongly inhibited activity. Thiore‐active agents inhibited activity indicating that a sulphydryl group is essential for activity. The enzyme was thermally inactivated at temperatures a

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1980.tb00785.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Black gram seeds and cotyledons from two origins, India and Thailand were evaluated for alpha‐amylase inhibitor and phytohemagglutinating activities. Alpha‐amylase inhibitor activity was absent in black gram seeds and cotyledons from two different origins. Phytohemagglutinating activity was not detected in the extracts of black gram seeds and cotyledons from two origins, tested against human A, rabbit, cow, and sheep blood erythrocy

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1980.tb00786.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY