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At least 235 records · Page 13Linked to original sources
PubMed1983

A reinvestigation on the quaternary structure of ascorbate oxidase from Cucurbita pepo medullosa.

The optical properties, copper content, catalytic activity and quaternary structure of many preparations of ascorbate oxidase purified with two different methods were examined. Fresh samples appeared identical and were characterized by optical ratios A280/A610 = 25 +/- 1 and A330/A610 = 0.8 +/- 0.05, by specific activity toward ascorbate of 3.48 +/- 0.05 mol g-1 min-1 and by a copper content of 8 +/- 0.3 mol/145 000 Mr. The enzyme is composed of two non-covalently linked subunits of slightly different molecular mass (75 000 and 72 000 respectively). These subunits cannot be further resolved by reduction of disulfide bonds. Proteolytic cleavage of the protein chains was observed during purification and storage in the absence of the protease inhibitor 6-amino caproic acid. Ascorbate oxidase exists as a monomer at neutral pH and undergoes reversible association into higher molecular weight species at slightly acid pH values. Association is not accompanied by spectroscopic or catalytic changes.

Ascorbate Oxidase↗
PubMed1990

Restriction site and genetic map of Cucurbita pepo chloroplast DNA.

A detailed restriction map of squash chloroplast DNA (cpDNA) was constructed with five restriction endonucleases, SalI, PvuII, BglI, SacII, and PstI. The cleavage sites were mapped by sequential digestion of cpDNA using low-gelling temperature agarose. The restriction map shows that squash cpDNA is an approximately 153 kilobase (kb) circle with a large inverted repeat sequence of 23.3 kb, separated by a large (83.7 kb) and a small (22.7 kb) single copy region. Genes for a number of chloroplast polypeptides were localized on the map by hybridizing the cpDNA restriction fragments to heterologous gene-specific probes from tobacco, pea, tomato, maize, and spinach chloroplasts. The gene locations and organization of squash cpDNA are highly conserved and similar to chloroplast genomes of tomato, pepper, and Ginkgo.

Chloroplasts↗
PubMed1996

Antigenotoxic spinasterol from Cucurbita maxima flowers.

The antigenotoxic constituent of squash flowers was isolated by solvent partitioning and repeated vacuum liquid chromatography. The micronucleus test, an in vivo method, was used to monitor the antigenotoxicity of the various fractions during the isolation process. Isolate SQFwB2D from the chloroform extract of squash flowers is the most antigenotoxic isolate. It decreased the mutagenicity of tetracycline by 64.7% at a dosage of 100 mg/kg mouse. Statistical analysis using Kruskall Wallis one-way analysis of variance by Ranks showed that SQFw2D is different from the control group (tetracycline + corn oil) at alpha = 0.001. GC-MSD of isolate SQFwB2D shows 2 peaks at Rt = 19.860 (SQFwB2D-1) and 20.242 min (SQFwB2D-2) with relative peak heights of 16:1, respectively. Spectral analyses show that SQFwB2D-1 is 24 alpha-ethyl-5 alpha-cholesta-7,trans-22-dien-3 beta-ol or spinasterol.

Animals↗
PubMed1998

Modifications outside the proteinase binding loop in Cucurbita maxima trypsin inhibitor III (CMTI-III) analogues change the binding energy with bovine beta-trypsin.

Five 26-peptide analogues of the trypsin inhibitor [Pro18]CMTI-III containing Leu or Tyr in position 7 and Val or Tyr in position 27: 1 (Leu7, Tyr27), 2 (Tyr7, Val27), 3 (Tyr7, Tyr27), 4 (Leu7, Val27) and 5 (Leu7, Ala18, Tyr27) were synthesized by the solid-phase method. Analogues 1-4 displayed Ka with bovine beta-trypsin of the same order of magnitude as the wild CMTI-III inhibitor, whereas for analogue 5, this value was lower by about 3 orders of magnitude. This indicated that for the analogues with Pro (but not with Ala) in position 18, the side-chain interactions between positions 7 and 27 did not play a critical role for the stabilization of the active structure. In addition, these results also suggest that Tyr7 is involved in an additional aromatic interaction with position 41 of the enzyme.

Amino Acid Sequence↗