Antilipolytic effect of prostaglandin E2 analogues: therapeutic implications.

15(S), 15 methyl PGE₂, methyl ester and 16,16 dimethyl PGE₂ are potent inhibitors of norepinephrine-induced lipolysis in isolated rat adipocytes, comparable to PGE₂. Because these methyl analogues of PGE₂ are antilipolytic but are not rapidly metabolized by 15 PG dehydrogenase, it is suggested that they may be potent antilipolytic agents in vivo and therefore potentially useful in the treatment of disorders with accelerated lipolysis such as diabetic ketoacidosis.     

Mesozoic paleogeography and early angiosperm history

During the Early Cretaceous, ocean-floor spreading gradually opened up the tropical Atlantic and the Indian Ocean basin widened as the eastern segments of Gondwanaland were conveyed farther apart. At the same time, epeiric seas were advancing on all continents, reaching maximum extent during the Cenomanian. The resultant trend to widespread, more equable climate favored the invasion into the lowlands of angiosperms whose postulated origin was in mild uplands at low latitudes during pre-Cretaceous times. As tropical and subtropical lands were rafted farther apart by ocean-floor spreading following Albian-Cenomanian times, new taxa (species, genera, tribes, families) evolved in isolation. This accounts in part for the increasing richness of the three major tropical floras following the Cretaceous. Changes in Mesozoic paleogeography also appear to clarify several other puzzling aspects of early angiosperm history and distribution, including their early appearance at middle latitudes.     

REGIONAL AND SUBCELLULAR DISTRIBUTION OF PROTEIN CARBOXYMETHYLASE IN BRAIN AND OTHER TISSUES

Protein carboxymethylase, an enzyme that transfcrs the methyl group of S-adenosyl-L-methionine to carboxyl groups of proteins and endogenous acceptor proteins were examined in nerve and endocrine tissues. The highest protein carboxymethylase activity was found in the brain, followed by the testis, pituitary and heart. On the other hand, the tissue with the highest level of endogenous substrate(s) was the pituitary. The nearly identical specific activity ratio for two different protein substrates in all tissues examined, suggests that one enzyme is responsible for carboxymethylase activity in different tissues. The subcellular distribution of the enzyme in brain showed a high concentration in the soluble fraction, presumably representative of the enzyme in the cytosol of cell bodies. Considerable enzyme activity was also found in brain synaptosomes which was increased by osmotic lysis. Protein carboxymethylase was shown to accumulate proximally to a ligation of the rat sciatic nerve. A possible physiological role for protein carboxymethylase in neuronal function is discussed.     

Dimethyl sulfoxide affects the amount of extrachromosomal spleen focus-forming virus DNA in murine erythroleukemia cells.

We used Southern blot hybridization to titrate and map restriction enzyme cleavage sites of a 6.3-kilobase-pair species of extrachromosomal viral DNA found in derivatives of the 745A line of murine erythroleukemia cells, which vary in their ability to be induced to differentiate by dimethyl sulfoxide (DMSO). Greater than an eightfold variation was observed in the amount of this DNA, with the largest amounts being found in cells that were resistant to the induction of differentiation by DMSO. This increase in the level of extrachromosomal viral DNA was found to be dependent upon the continued presence of DMSO in the culture medium. The increase was shown not to be due to an immediate stimulatory effect of this agent on the synthesis or maintenance of this DNA, since cell lines sensitive to the differentiation-inducing effects of DMSO were shown to undergo a transient reduction in the amount of extrachromosomal viral DNA after the addition of DMSO to the culture medium. In addition to the 6.3-kilobase-pair linear form found in the cytoplasm, in some preparations two hybridizing bands were observed that migrated in agarose gels in the position expected of covalently closed circular species of viral DNA. Restriction enzyme mapping of the cytoplasmic linear form indicated a close relationship of this DNA to two polycythemic strains of spleen focus-forming virus that have been molecularly cloned by other workers. No obvious change in the number or arrangement of chromosomal viral sequences could be detected after treating cells with DMSO. Thus, the exposure of murine erythroleukemia cells to DMSO caused an obvious change in the amount of extrachromosomal spleen focus-forming virus DNA but no obvious change in the integration of the provirus.     

Maintenance of hemoglobin inducibility in somatic cell hybrids of tetraploid (2S) mouse erythroleukemia cells with mouse or human fibroblasts.

It has previously been reported that Friend mouse erythroleukemia (MEL) cells synthesize hemoglobin when exposed to 2% dimethylsulfoxide, and that hybrids between MEL cells and fibroblasts (or other nonerythroid cells) do not synthesize hemoglobin. We have been successful in obtaining hybrids (3/15) between MEL cells and mouse L-cell fibroblasts that maintain hemoglobin inducibility by preserving nonadherent cells after fusion. The proportion of hemoglobin inducible hybrids can be increased (8/11) by using a stable 2S (pseudotetraploid) MEL parent in addition to preserving nonadherent cells after fusion. All hybrids which were nonadherent were hemoglobin inducible, and all hybrids which were adherent were not. Five nonadherent hybrid clones were analyzed from fusions between a stable 2S MEL parent and a human fibroblast (WI-38, VA-2). All these clones were inducible for hemoglobin. It is concluded that gene dosage is effective in increasing the proportion of hemoglobin inducible hybrids, but hybrid morphology is the phenotype characteristic that correlates most closely with expression of hemoglobin inducibility.     

DOPAMINE-β-HYDROXYLASE IN THE RAT BRAIN: DEVELOPMENTAL CHARACTERISTICS

Abstract— A sensitive and specific assay for dopamine-8-hydroxylase (DBH) in the rat brain has been developed. The enzyme in the brain has requirements for cofactors and affinity for substrate similar to DBH in the adrenal medulla. DBH activity was demonstrable in the brain of the fetal rat at 15 days of gestation; there was an increase in DBH activity with maturation that preceded and paralleled the rise in levels of endogenous norepinephrine until 3 weeks after birth. There was a shift in the distribution of total DBH activity from the caudal to the rostral regions of the brain during development. In the adult brain, DBH was highly localized in the nerve terminals. Between 17 days of gestation and adult-hood, there was 2300-fold increase in the DBH activity that sedimented with sheared-off nerve terminals.     

Effect of ferrate, a site-specific phosphate analog, on human deoxyhemoglobin

Ferrate ion, a phosphate analog and a potent oxidizing agent, is known to inactivate a number of enzymes which interact with phosphoryl compounds. In contrast, enzymes which do not interact with phosphoryl compounds are not affected by comparable concentrations of ferrate. To further explore the specificity of ferrate as a reagent which is specific for phosphoryl binding sites, a study of its effect on human hemoglobin A was undertaken. In the deoxy form, this protein is known to interact with 2,3-bisphosphoglycerate, its natural allosteric inhibitor of cooperative binding of oxygen, while as oxyhemoglobin it does not interact with the inhibitor. Treatment with ferrate ion caused the loss of approximately three amino acid residues per beta chain of human deoxyhemoglobin, His-2, His-143, and Tyr-145, and one residue, presumably Tyr-42, per alpha chain. Oxyhemoglobin was not affected by the reagent. 2,3-Bisphosphoglycerate was found to protect deoxyhemoglobin from the action of ferrate. His-2 and His-143 are among the residues reported to be implicated in the binding of 2,3-bisphosphoglycerate by deoxyhemoglobin [A. Arnone (1972) Nature (London) 237, 146-148].