Ferrochelatase of spinach chloroplasts

Spinach chloroplasts catalyse the incorporation of Fe2+ into protoporphyrin, mesoporphyrin and deuteroporphyrin to form the corresponding haems. This ferrochelatase activity was detected by pyridine haemochrome formation with acetone-dried powders of chloroplasts, or from the formation of [59Fe]haems by intact chloroplasts. Decreasing the mitochondrial contamination of the chloroplasts by density-gradient centrifugation did not cause any loss of activity: spinach ferrochelatase appears to be principally a chloroplast enzyme. The characteristics of the enzyme were examined by using [59Fe]haem assay. The activity was pH-dependent: for both mesohaem and protohaem formation there were two pH maxima, a major peak at about pH7·8 and a smaller peak at about pH9·2. Lineweaver–Burk plots showed that the Km for Fe2+ incorporation into protoporphyrin was 8μm and that for Fe2+ incorporation into mesoporphyrin was 36μm. At non-saturating Fe2+ concentrations the Km for protoporphyrin was 0·2μm and that for mesoporphyrin was 0·4μm. Ferrochelatase was not solubilized by treatment of chloroplasts with ultrasound but was solubilized by stirring in 1% (w/v) Tween 20 at pH10·4. Unlike the rat liver mitochondrial enzyme, chloroplast ferrochelatase was not stimulated by treatment with selected organic solvents. The spinach enzyme was inactive in aerobic conditions and it was shown by using an oxygen electrode that under such conditions the addition of Fe2+ to buffer solutions caused a rapid uptake of dissolved oxygen, believed to be due to the oxidation of Fe2+ to Fe3+; Fe3+ is not a substrate for ferrochelatase.

Download Full-text

Uranyl Acetate and Rotary Shadowing to Increase the Contrast of Small Aggregated Virus Particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100064037 ◽

1969 ◽

Vol 27 ◽

pp. 424-425

Author(s):

Lee F. Ellis ◽

Richard M. Van Frank ◽

Walter J. Kleinschmidt

Keyword(s):

Electron Microscopy ◽

Tissue Culture ◽

Density Gradient ◽

Density Gradient Centrifugation ◽

Gradient Centrifugation ◽

Uranyl Acetate ◽

Interferon Inducer ◽

Virus Particles ◽

Staining Methods ◽

Rotary Shadowing

The extract from Penicillum stoliniferum, known as statolon, has been purified by density gradient centrifugation. These centrifuge fractions contained virus particles that are an interferon inducer in mice or in tissue culture. Highly purified preparations of these particles are difficult to enumerate by electron microscopy because of aggregation. Therefore a study of staining methods was undertaken.

Download Full-text

The Combining Ability of Glycoproteins IIb, IIIa and Ca2+ in EDTA-Treated Nonaggregable Platelets

Thrombosis and Haemostasis ◽

10.1055/s-0038-1665326 ◽

1983 ◽

Vol 50 (04) ◽

pp. 848-851 ◽

Cited By ~ 11

Author(s):

Marjorie B Zucker ◽

David Varon ◽

Nicholas C Masiello ◽

Simon Karpatkin

Keyword(s):

Density Gradient ◽

Combining Ability ◽

Density Gradient Centrifugation ◽

Gradient Centrifugation ◽

Electrophoretic Pattern ◽

Sucrose Density Gradient ◽

Irreversible Loss ◽

Sucrose Density Gradient Centrifugation ◽

Crossed Immunoelectrophoresis ◽

Triton X

SummaryPlatelets deprived of calcium and incubated at 37° C for 10 min lose their ability to bind fibrinogen or aggregate with ADP when adequate concentrations of calcium are restored. Since the calcium complex of glycoproteins (GP) IIb and IIIa is the presumed receptor for fibrinogen, it seemed appropriate to examine the behavior of these glycoproteins in incubated non-aggregable platelets. No differences were noted in the electrophoretic pattern of nonaggregable EDTA-treated and aggregable control CaEDTA-treated platelets when SDS gels of Triton X- 114 fractions were stained with silver. GP IIb and IIIa were extracted from either nonaggregable EDTA-treated platelets or aggregable control platelets with calcium-Tris-Triton buffer and subjected to sucrose density gradient centrifugation or crossed immunoelectrophoresis. With both types of platelets, these glycoproteins formed a complex in the presence of calcium. If the glycoproteins were extracted with EDTA-Tris-Triton buffer, or if Triton-solubilized platelet membranes were incubated with EGTA at 37° C for 30 min, GP IIb and IIIa were unable to form a complex in the presence of calcium. We conclude that inability of extracted GP IIb and IIIa to combine in the presence of calcium is not responsible for the irreversible loss of aggregability that occurs when whole platelets are incubated with EDTA at 37° C.

Download Full-text