Changes in predominant energy substrate after hepatectomy

The changes in the energy substrate utilized by the remnant liver were studied in relation to the changes in the cellular energy status of 25 and 70% hepatectomized rabbits. In 25% hepatectomized rabbits, the energy charge $\text{(}\text{(}\text{ATP}\text{+0.5}\text{ADP}\text{)}\text{(}\text{ATP}\text{+}\text{ADP}\text{+}\text{AMP}\text{)}\text{)}$ level of the remnant liver remained unchanged, the energy substrate of which was predominantly glucose, rather than fatty acid. In contrast, in 70% hepatectomized rabbits, the energy production by the mitochondria was mainly dependent upon fatty acid oxidation at the early period after hepatectomy when the energy charge level decreased remarkably, and then upon glucose oxidation, concomitant with the restoration of the energy charge. It is suggested that the changes in the energy substrate utilized are closely related to those in the energy charge level and the mitochondrial phosphorylative activity of the remnant liver following hepatectomy.     

Chemical Modification of the Membrane-bound ATP Synthetase of Spinach Chloroplasts with Pyridoxal Phosphate in Light

Photosynthetic activities of the thylakoid membranes modifiedwith pyridoxal phosphate (PLP) and sodium borohydride in lightwere studied and compared with those modified in the dark. PLPmodified the membrane-bound chloroplast coupling factor 1 (CF₁)and inhibited photophosphorylation. Only PLP modification inlight stimulated basal electron transport. This stimulationof electron transport was prevented by the presence of ATP orcarbonylcyanide m-chlorophenylhydrazone in the modificationmixture. Magnesium ion was required for PLP modification. Theextent of lightinduced proton uptake was decreased by PLP modificationin light. N,N'-Dicyclohexylcarbodiimide lowered the stimulatedelectron transport to the basal level of unmodified chloroplastsand restored proton uptake. When chloroplasts were modified with 4 mM PLP in light and dark,11.6 and 11.0 mol of PLP were incorporated into mol of CF₁,respectively. ATP could bind with high affinity to CF₁ isolatedafter PLP modification in light. The results indicate that PLP modifies membrane-bound CF₁ whichhas a conformation altered by energization of the thylakoidsin light, and causes an apparent uncoupling of phosphorylation(stimulation of basal electron transport). The results suggestthat this uncoupling is induced by the loss of the regulatoryfunction of CF₁ for proton translocation after PLP modificationin light. ¹ Presented at the ISRACON on Control Mechanisms in Photosynthesis.Aug. 31-Sept. 4, 1980, Acre, Israel (Received June 22, 1981; Accepted August 28, 1981)     

Ceramide metabolism in brain

Summary Ceramide is the fundamental structure and key intermediate of all sphingolipids. Biosynthesis and catabolism of brain ceramide, especially their relationship to the metabolism of more complex sphingolipids in brain, are reviewed. Human genetic diseases which involve altered ceramide metabolism are also discussed.     

Fatty acid α-hydroxylation and its relation to myelination

Summary -Hydroxylation is an enzymatic reaction by which long-chain fatty acids are converted to their -hydroxy derivatives. This reaction, in animals, can be detected only in developing brain and is the rate-determining step in the synthesis of hydroxycerebroside, which is an indispensable and abundant myelin lipid. In addition to a particulate fraction from brain, two cytoplasmic factors, one heat-stable and the other heat-labile, are required for -hydroxylation. During the past eight years we have been investigating -hydroxylation. Our progress is summarized and discussed here.     

Adenylate regulation of photosynthetic electron transport and the coupling sites of phosphorylation in spinach chloroplasts

The regulation by adenylates of activities of various partial electron transport systems in spinach chloroplasts was studied using systems from H₂O to 2,5-dimethyl-p-benzoquinone, H₂O to 2,6-dichlorophenolindophenol, reduced 2,6-dichlorophenolindophenol to methyl viologen, and H₂O to methyl viologen or ferricyanide. Adenylates regulated all of them. The ratio of the amount of esterified Pi (P) to that of electrons transported (e) in coupling with phosphorylation manifested that there are two phosphorylation sites: one between H₂O and 2,5-dimethyl-p-benzoquinone or 2,6-dichlorophenolindophenol and another between reduced 2,6-dichlorophenolindophenol and methyl viologen, under the proposed stoichiometries,i.e., P/H⁺=0.5 and H⁺/e=1, where H⁺ is the amount of protons pumped by electron transport (= those translocated during phosphorylation), when the basal electron transport (the part not regulated by adenylates) was excluded. The effects of pH, phlorizin, and methylamine on the adenylate regulation of electron transport, and the stimulation profile of electron transport coupled with quasiarsenylation suggested no distinction between the two phosphorylation sites.     

Biochemical evidence of DNA transport from the silk gland to the fat body of the silkworm, Bombyx mori

β-DNA, a component of DNA found in the pupal fat body of the silkworm, Bombyx mori, has the same GC content but a smaller molecular weight than typical silkworm DNA (α-DNA). Its origin and time of synthesis were studied by MAK column chromatography of phenol extracts after labelling with radioactive precursors.The DNA components of the fat body changed greatly during the early pupal stage, the β-DNA showing a striking increase relative to α-DNA. Thymidine-6-³H and phosphoric acid-³²P injected into the animals 1 day before analysis caused labelling of α-DNA, but not of β-DNA of the fat body, indicating that β-DNA was not synthesized during the stage of its appearance in the fat body.On the other hand, injection of thymidine-6-³H into 2-day-old fifth instar larvae, when DNA of the silk gland was being actively synthesized, gave high incorporation of the isotope into β-DNA of the pupal fat body. The sudden appearance of highly labelled β-DNA in the fat body during the early pupal stage as well as the occurrence of β-DNA in both the silk gland and fat body suggested that DNA might move from the silk gland to the fat body.It is possible that the fat body stores DNA as a nutrient from the degenerating silk gland.     

Inhibition and uncoupling of the ADP-regulated electron transport in isolated chloroplasts

The effects of energy transfer inhibitors, electron transport inhibitors and uncouplers on the ADP-regulated and ADP-independent activity of ferricyanide reduction in isolated spinach chloroplasts were studied. Phlorizin and sulfate did not affect the ADP-independent ferricyanide reduction. In the ADP-regulated reduction, these reagents did not affect the ADP inhibition process but inhibited the activity restoration process due to phosphorylation. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea and linolenic acid depressed both ADP-regulated and ADP-independent activity of ferricyanide reduction. Gramicidin S and 2-amino-1-butanol depressed ADP-regulated activity and stimulated ADP-independent activity. The decrease in the ADP-regulated ferricyanide-reducing activity (restoration) due to (incomplete) uncoupling paralleled the decrease in phosphorylation activity (P/Δe=1).