Establishment and characterization of a bi-phenotypic leukemic cell line, NALM-19, from a patient with acute leukemia.

Based on the immunophenotypic and genotypic findings, this acute leukemia cell line, designated NALM-19, is unique in that a partial expression of both B-cell and myeloid cell features are present in this single clonal leukemic cell population. It is noteworthy that two "normal" EB virus-transformed B cell lines, B239 and B240, (paired with NALM-19) were established from the same leukemic blood.     

Hydrogen exchange kinetics of nucleic acids: Double and triple helices with Hoogsteen-type basepairs

The kinetics of hydrogen-tritium exchange reaction have been followed by a Sephadex technique of a double-helical poly(ribo-2-methylthio-adenylic acid)·poly(ribouridylic acid) complex with the Hoogsteen-type basepair. Only one hydrogen in every 2-methylthio-adenine·uracil basepair has been found to exchange at a measurably slow rate, 0.023 s^?1 (at 0°C), which is, however, much greater than that for a double-helix with the Watson-Crick type A·U pair. The kinetics of hydrogen-tritium exchange were also examined by triple-helical poly(rU)·poly(rA)·poly(rU) which involves both the Watson-Crick and Hoogsteen basepairings. Here, three hydrogens in every U·A·U base triplet have been found to exchange at a relatively slow rate, 0.0116 s^?1 (at 0°C). The kinetics of hydrogen-deuterium exchange reactions of these polynucleotide helices have also been followed by a stopped-flow ultraviolet absorption spectrophotometry at various temperatures. On the basis of these experimental results, the mechanism of the hydrogen exchange reactions in these helical polynucleotides was discussed. In the triple helix, the rate-determining process of the slow exchange of the three (one uracil-imide and two adenine-amino) hydrogens is considered to be the opening of the Watson-Crick part of the U·A·U triplet. This opening is considered to take place only after the opening of the Hoogsteen part of the triplet.     

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)     

Contribution from the chirality of the growing chain to the enantiomer selectivity in activated-NCA polymerization of α-amino acid N-carboxyanhydride

As a model compound for the growing chain in the activated-NCA type of polymerization of α-amino acid N-carboxyanhydride (NCA), 3-[ω-acetylglycyl-poly(α-amino acid) acyl]-α-amino acid NCA (called the prepolymer) having various degrees of polymerization (DPs) was synthesized by the polymerization of Phe, Val, Glu(OEt), and Asp(OBzl) NCA in the presence of AcGly NCA by the tertiary amine. Activated (S)-Phe, Val, Glu(OEt), and Asp(OBzl) NCA were added to the terminal cyclic group of the corresponding (S)- or (R)- prepolymer, and the enantiomer selectivity in the reaction was investigated. With prepolymers having DPs ranging from 1 to 15, the addition reaction always took place preferentially between species having the same configuration, and the degree of the enantiomer selection increased with increasing DP of the prepolymer. With prepolymers having DP = 1 and 2, we found contributions from the chiral terminal unit and the chiral penultimate unit to the enantiomer selection, respectively. Prepolymer having DP = 5 was shown to take a β-type conformation, which led to higher enantiomer selection; and prepolymers having DP = 10 and 15 were shown to take an α-helix conformation, which led to much higher enantiomer selection than did the β-type conformation. In the present investigation the mechanisms of terminal-unit control, penultimate-unit control and conformational control of the enantiomer selection in the activated-NCA type of polymerization were clearly observed.     

The initiation of fetal hemoglobin biosynthesis.

Biosynthesis of the alpha and beta chains of rabbit and human adult hemoglobin is initiated with a methionyl residue, which is removed during elongation of the peptide chain. To study the initiation of biosynthesis of the delta chain of human fetal hemoglobin, fresh placental blood was used for labeling experiments with radioactive amino acids. Labeled nascent peptide chains were purified from the polysomal fraction of placental blood reticulocytes. The number of amino acid residues in nascent gamma chain at the time of removal of its N-terminal methionine was estimated to be 40--60 from the relative yields of labeled tryptic peptides.     

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.