Studies on the adrenal cortex of hypophysectomized rats: A model for abnormal cellular atrophy and death

Summary Biochemical and ultrastructural studies indicate that the atrophy of adrenal cortex in hypoyhysectomized rats involves the following changes: (1) One to two days after hypophysectomy, there is loss of template activity resulting from cumulative DNA-damage and heterochromatinization.In vivo ACTH-administration led to recuperation of these cells, indicating damage during hypophysectomized state to be reversible. (2) If the duration of hypophysectomy is prolonged, some of the cells become irreversibly damaged and can no longer recuperate afterin vivo ACTH administration. (3) The period of most rapid cell death is from the third to seventh day after hypophysectomy. The cause of cell death is probably due to membrane damage in the absence of protein synthesis, leading to lysis of the cells. Lysozomes and macrophages are apparently not involved.Supported by U.S.P.H.S. grants AM-5384 and AM-13724 and taken in part from dissertations submitted by Chan and by Mostafapour to Wayne State University in partial fulfillment towards the Ph.D. degree.An invited article.     

Photosynthetic Pod Wall of Pea (Pisum sativum L.): Distribution of Carbon Dioxide-fixing Enzymes in Relation to Pod Structure

The pod wall of pea (Pisum sativum L.) was shown to contain two distinct photosynthetic layers. The outer, comprising chlorenchyma of the mesocarp, captured CO₂ from the outside atmosphere; the inner, a chloroplast-containing epidermis lining the pod gas cavity, was involved in photoassimilation of the CO₂ released from respiring seeds.     

Characterization of leukotriene A4 and B4 bioysnthesis

We have studied LTA₄ and LTB₄ synthesis in a cell-free system from RBL-1 cells. All the enzymes leading to the formation of LTB₄ from arachidonic acid are localized in the soluble fraction (100, 000 x g supernatant) of these cells. The formation of LTA₄ and LTB₄ is complete by 10 min. When we varied the arachidonic acid concentration from 1 to 300 μM, the synthesis of LTB₄ leveled off at 30 μM and of LTA₄ at 100 μM while 5-HETE had not reached a plateau at 300 μM. This enzyme system has the capacity to generate relatively large amounts of 5-HETE and LTA₄ and only a relatively small amount of LTB₄. Therefore, the rate limiting step is not the 5-lipoxygenase, the first step in the pathway, but the conversion of LTA₄ to LTB₄. This is in contrast to cyclooxygenase pathway where the first step is rate limiting. A second addition of arachidonic acid at submaximal concentration for LTA₄ synthesis did not produce any additional LTA₄ or LTB₄. Further study of this phenomenon showed that the 5-lipoxygenase and LTA-synthase were inactivated with time by preincubation with arachidonic acid and that peroxy fatty acids seem to be the inactivating species.     

Mitotic arrest and enhanced nuclear protein phosphorylation in human leukemia K562 cells by okadaic acid, a potent protein phosphatase inhibitor and tumor promoter.

We investigated the effects of the non-phorbol tumor promoter okadaic acid on human leukemia K562 cells. It was found that okadaic acid potently and reversibly inhibited cell growth, with a nearly complete inhibition of thymidine uptake seen at about 10 nM. The cytotoxicity of okadaic acid was characterized by a marked mitotic arrest of the cells exhibiting scattered chromosomes and abnormal anaphase-like structures, a phenomenon distinct from the typical metaphase arrest caused by colchicine. Okadaic acid (10-1,000 nM) greatly stimulated phosphorylation of a number of nuclear proteins in K562 cells. Phosphorylation of many of the same proteins was also stimulated by 12-O-tetradecanoylphorbol-13-O-acetate, a protein kinase C activator. The present findings, consistent with recent reports that okadaic acid is a potent inhibitor of protein phosphatases 1 and 2A (PP1 and PP2A) shown to be essential for normal mitosis, provided evidence for the first time that okadaic acid inhibition of PP1/PP2A resulted in enhanced nuclear protein phosphorylation and subsequent mitotic arrest.     

Membrane interactions of mastoparan analogues related to their differential effects on protein kinase C, Na, K-ATPase and HL60 cells.

Membrane interactions of tetradecapeptide toxin mastoparan (MP) and analogues (MP-3, MP-X and polistes MP), as indicated by inhibition of various enzymatic and cellular activities, were investigated. MP-3 was found to be the least active in inhibiting protein kinase C (PKC; activated by phosphatidylserine vesicles, synaptosomal membranes or phorbol ester), synaptosomal membrane Na,K-ATPase and proliferation and viability of leukemia HL60 cells. MP-3, however, was as active as others in inhibiting PKC activated by arachidonate monomers and phorbol ester binding. The unique properties of MP-3, the [des-Ile1-Asn2]-analogue of MP, might be related to its low functional amphiphilicity compared to others and useful in further delineating biological activities associated with or regulated by membranes.     

Characterization of the zinc binding site of bacterial phosphotriesterase.

The bacterial phosphotriesterase has been found to require a divalent cation for enzymatic activity. This enzyme catalyzes the detoxification of organophosphorus insecticides and nerve agents. In an Escherichia coli expression system significantly higher concentrations of active enzyme could be produced when 1.0 mM concentrations of Mn2+, Co2+, Ni2+, and Cd2+ were included in the growth medium. The isolated enzymes contained up to 2 equivalents of these metal ions as determined by atomic absorption spectroscopy. The catalytic activity of the various metal enzyme derivatives was lost upon incubation with EDTA, 1,10-phenanthroline, and 8-hydroxyquinoline-5-sulfonic acid. Protection against inactivation by metal chelation was afforded by the binding of competitive inhibitors, suggesting that at least one metal is at or near the active site. Apoenzyme was prepared by incubation of the phosphotriesterase with beta-mercaptoethanol and EDTA for 2 days. Full recovery of enzymatic activity could be obtained by incubation of the apoenzyme with 2 equivalents of Zn2+, Co2+, Ni2+, Cd2+, or Mn2+. The 113Cd NMR spectrum of enzyme containing 2 equivalents of 113Cd2+ showed two resonances at 120 and 215 ppm downfield from Cd(ClO4)2. The NMR data are consistent with nitrogen (histidine) and oxygen ligands to the metal centers.