scispace - formally typeset
Search or ask a question
Author

Irwin W. Sizer

Other affiliations: Argonne National Laboratory
Bio: Irwin W. Sizer is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Tyrosinase & Catalase. The author has an hindex of 24, co-authored 59 publications receiving 7753 citations. Previous affiliations of Irwin W. Sizer include Argonne National Laboratory.


Papers
More filters
Journal ArticleDOI
TL;DR: A quantitative, spectrophotometric technique for following the breakdown of hydrogen peroxide has been developed for routine studies of catalase kinetics and appears to give lower values forCatalase activity than do titration techniques.

6,007 citations

Journal ArticleDOI
TL;DR: The first reaction product of tyramine, horse-radish peroxidase, and hydrogen peroxide has been shown to be 2,2”-dihydroxy-5,5’-bis(ðylamino) diphenyl (I), referred to as dityramine.

359 citations

Journal ArticleDOI
TL;DR: The use of substrate amounts of enzyme permits the spectroscopic identification of active and inert enzyme complexes over a wide pH range and is analogous to that which leads to the formation of a new amino acid (i.e. that between aspartate and ketoglutarate).

141 citations

Journal ArticleDOI
TL;DR: The data obtained so far support the contention that the oxidation of leucine, as well as other l -α-amino acids, may be attributed to the nonspecific action of l -glutamic acid dehydrogenase.

103 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: A quantitative, spectrophotometric technique for following the breakdown of hydrogen peroxide has been developed for routine studies of catalase kinetics and appears to give lower values forCatalase activity than do titration techniques.

6,007 citations

Journal ArticleDOI
Asru K. Sinha1
TL;DR: A simple colorimetric assay for catalase activity has been described using K2Cr2O7/acetic acid reagent to determine values of different enzyme sources and compared with the values obtained by titrimetric methods.

4,827 citations

Book ChapterDOI
TL;DR: Two methods are described for the catalase assay by disappearance of peroxide are: ultraviolet spectrophotometry and permanganate titration and indirect measurements of the decrease of light absorption caused by the decomposition of hydrogen peroxide byCatalase.
Abstract: Publisher Summary This chapter discusses the assay of catalases and peroxidases are: (1) catalase assay by disappearance of peroxide; (2) method for crude cell extracts; (3) direct spectrophotometric assay of catalase and peroxidase in cells and tissues; and (4) peroxidase assay by spectrophotometric measurements of the disappearance of hydrogen donor or the appearance of their colored oxidation products. Two methods are described for the catalase assay by disappearance of peroxide are: ultraviolet spectrophotometry and permanganate titration. Ultraviolet spectrophotometryis a method devised, on the basis of the absorption curves for peroxide solutions, for determining the activity of catalase by direct measurements of the decrease of light absorption in the region 230 to 250 mμ caused by the decomposition of hydrogen peroxide by catalase. In the case of method for crude cell extracts, oxygen evolution caused by the decomposition of hydrogen peroxide is measured with the conventional manometric technique. Peroxidase assay by spectrophotometric measurements of the disappearance of hydrogen donor or the appearance of their colored oxidation products includes the guaiacol test and the pyrogallol test.

3,917 citations

Journal ArticleDOI
TL;DR: The relationship between antioxidant activity and antimutagenicity of various tea extracts (green tea, pouchong tea, oolong tea and black tea) was investigated in this article, which showed that all tea extracts exhibited markedly antioxidant activity.
Abstract: The relationship between antioxidant activity and antimutagenicity of various tea extracts (green tea, pouchong tea, oolong tea, and black tea) was investigated. All tea extracts exhibited markedly antioxidant activity and reducing power, especially oolong tea, which inhibited 73.6% peroxidation of linoleic acid. Tea extracts exhibited a 65-75% scavenging effect on superoxide at a dose of 1 mg and 30 - 60% scavenging effect on hydrogen peroxide at a dose of 400 microgram. They scavenged 100% hydroxyl radical at a dosage of 4 mg except the black tea. Tea extracts also showed 50 - 70% scavenging effect on alpha, alpha-diphenyl-beta-picrylhydrazyl radical. The antioxidant activity and the scavenging effects on active oxygen decreased in the order semifermented tea > nonfermented tea > fermented tea. Tea extracts showed strong antimutagenic action against five indirect mutagens, i.e., AFB1, Trp-P-1, Glu-P-1, B[a]P, and IQ, especially oolong and pouchong teas. The antioxidant effect of tea extracts was well correlated to their antimutagenicity in some cases but varied with the mutagen and antioxidative properties.

2,436 citations

Journal ArticleDOI
TL;DR: With a Stokes radius measured by the chromatographic method and a sedimentation coefficient determined by density gradient centrifugation, reasonable estimates for both the molecular weight and the frictional ratio (f/f0) of a macromolecule are available.

2,116 citations