Effects by heme, insulin, and serum albumin on heme and protein synthesis in chick embryo liver cells cultured in a chemically defined medium, and a spectrofluorometric assay for porphyrin composition.

Hemes, chlorophylls, and related compounds: biosynthesis and metabolic regulation.

Study of intracellular iron distribution in rabbit reticulocytes with normal and inhibited heme synthesis.

Binding of heme by glutathione S-transferase: a possible role of the erythrocyte enzyme.

As a model for the transport of hemin across biological membranes, sonicated phosphatidylcholine liposomes with incorporated hemin were characterized. The interaction of the hemin liposomes with the heme binding proteins albumin, apomyoglobin, and hemopexin was examined as a function of liposome charge and cholesterol content. In all cases, there was an almost complete transfer of hemin from liposome to protein; a rapid phase and a slow phase were observed for the transfer. For negatively charged liposomes (with 11% dicetyl phosphate), the rapid and slow phases showed observed rates of transfer of ca. 2 and 0.01 s-1, respectively, for all three proteins. The presence of cholesterol in the liposomes decreased the observed rates by a factor of 2, and positively charged liposomes (with 11% stearylamine) showed about one-fifth the observed rates of negatively charged liposomes. The observed rates were independent of protein concentration, indicating that the rate-determining step is hemin efflux from the lipid bilayer. The hemin interaction with the phospholipid bilayer is suggested to be primarily hydrophobic with some electrostatic character. The two phases are suggested to arise from two different populations of hemin within the liposomes and are interpreted as arising from two different orientations of hemin within the bilayer.

Kinetics of the interaction of hemin liposomes with heme binding proteins.

The final steps in heme synthesis take place within mitochondria while the acceptor apoproteins are synthesized on the endoplasmic reticulum. When 14C-δ-aminolevulinic acid is used as a heme precursor in intact rats, measurable 14C-heme is found to be associated with the microsomes within 10 min of intraperitoneal injection. This rapid transfer of heme from mitochondria was studied in vitro using isolated rat liver mitochondria, and protoporphyrin IX and 59Fe as heme precursors. These mitochondria synthesize heme when suspended in whole cell sap and this is only partially reduced by substituting Sephadex G-25 filtered cell sap or sucrose. Mitochondria incubated in G-25 filtered cell sap or sucrose synthesize equivalent amounts of heme but those in sucrose export little heme into the surrounding medium. Heme export from mitochondria is dependent on protein in the suspending medium. In cell sap, heme is associated with multiple proteins and no single carrier was identified. Heme probably makes its way from ...

L G Israels

Papers

Transfer of Heme from Mitochondria in Rat Liver Cells