Prostaglandin oligomeric derivatives inhibit in vitro formation of dehydrated cells from sickle red cells

Two types of oligomeric derivatives of prostaglandin E1 were synthesized, a free-acid type and a lipophilic ester type. Neither compound inhibited sickling of red blood cells from sickle cell anaemia patients. However, both were found to inhibit the in vitro formation of dehydrated, dense cells (DC) caused by repeated cycles of sickling and unsickling of sickle cells. Both inhibited the formation of DC in a dose-related manner, but the ester type compound was more effective than the acid-type compound. Concentrations at which these compounds inhibit the DC formation by 50% were 5.2 microM and 40 microM for ester and free-acid compounds, respectively. A possible inhibition mechanism is discussed.     

Aldosterone biosynthesis and cytochrome P-45011 beta: evidence for two different forms of the enzyme in rats

Whereas cytochrome P-45011 beta has been recently shown to catalyze the two-step conversion of corticosterone to aldosterone in the bovine and porcine adrenal cortex, the identity of the enzyme involved in the two final steps of aldosterone biosynthesis in the rat adrenal cortex is as yet unknown. Mitochondria from capsular adrenals of sodium-deficient, potassium-replete rats converted corticosterone to 18-hydroxycorticosterone and aldosterone at markedly higher rates than mitochondria from capsular adrenals of sodium-replete, potassium-deficient rats. However, the same preparations exhibited no difference in the 11 beta-hydroxylase activity, i.e. the conversion of deoxycorticosterone to corticosterone. Only mitochondria of zona glomerulosa from rats with stimulated aldosterone biosynthesis contained a 49K protein which showed a strong cross-reactivity with a monoclonal antibody raised against purified bovine cytochrome P-45011 beta. By contrast, a crossreactive protein with a molecular weight of 51K was found in mitochondria of zona fasciculata and in mitochondria of zona glomerulosa from rats with a suppressed aldosterone biosynthesis. These findings indicate the existence of two different forms of cytochrome P-45011 beta in the rat adrenal cortex, with only one of them, i.e. the 49K form, being capable of catalyzing the two final steps of aldosterone biosynthesis in situ.     

Identification of flagellar hook and basal body gene products (FlaFV, FlaFVI, FlaFVII and FlaFVIII) in Salmonella typhimurium.

The flagellar genes flaFV, flaFVII, and flaFVIII of Salmonella typhimurium were cloned, and their presence on a given plasmid was verified by complementation of Escherichia coli mutants defective in the homologous genes. The gene products were identified by radiolabeling in a minicell system as being proteins of the following molecular masses: FlaFV, 42 kilodaltons (kDa); FlaFVI, 32 kDa; FlaFVII, 30 kDA; and FlaFVIII, 27 kDa. These data, together with isoelectric focusing data, confirm gene product assignments of flagellar components made indirectly from mutant studies. Flagellar components are transported by either a signal peptide-dependent or a flagellar-specific pathway. Consistent with its location in the outer membrane ring of the basal body, protein FlaFVIII seems to use the signal peptide-dependent pathway, since it was synthesized in a precursor form and processed, presumably by peptide cleavage, to a mature form; the maturation process was inhibited by addition of a proton ionophore. Proteins synthesized in minicells were localized as follows: FlaFVI was localized to the soluble fraction (cytoplasm); pre-FlaFVIII and FlaFVIII were localized to the particulate fraction (membrane or high-molecular-weight aggregate); FlaFV and FlaFVII were localized to both fractions. The significance of these locations in terms of known or suspected roles in the flagellar apparatus is discussed.     

Phosphorylation sites of bovine brain myelin basic protein phosphorylated with Ca2+-calmodulin-dependent protein kinase from rat brain

The phosphorylation sites of myelin basic protein from bovine brain were determined after phosphorylation with Ca2+-calmodulin-dependent protein kinase. Four phosphorylated peptides were selectively and rapidly separated by reversed-phase high-performance liquid chromatography. Partial sequencing of the phosphorylated peptides by automated Edman degradation revealed that Ca2+-calmodulin-dependent protein kinase phosphorylated serine-16, serine-70, and threonine-95 specifically, as well as serine-115, which is located on the experimental allergic encephalitogenic determinant of the protein. Of the four amino acid sequences determined, two sequences surrounding phosphorylated amino acids, -Lys-Tyr-Leu-Ala-Ser(P)16-Ala- and -Arg-Phe-Ser(P)115-Trp-Gly-, have both sides of each phosphoserine residue occupied by hydrophobic amino acids, and a basic amino acid, arginine or lysine, is located at the position 2 or 4 residues amino-terminal to the phosphoserine residue. In contrast, the two other sequences surrounding phosphorylated amino acids, -Tyr-Gly-Ser(P)70-Leu-Pro-Glu-Lys- and -Ile-Val-Thr(P)95-Pro-Arg-, have a basic amino acid at the position 2 or 4 residues carboxyl-terminal to the phosphoamino acid residue.     

Calcium ionophoretic activity of chemically synthesized oligomeric derivatives of prostaglandin B1

Chemically synthesized dimers, trimers and tetramers of 15-dehydroprostaglandin B1 and 16,16'-dimethyl-15-dehydroprostaglandin B1 facilitate the release of Ca2+ from isolated rat liver mitochondria. The parent monomeric prostaglandins had no significant activity. The rate of release was stimulated by exogenous K+ or Na+, suggesting an antiport exchange of monovalent cations for intra-mitochondrial Ca2+. The activity depended upon the presence of ruthenium red, which prevented recycling of Ca2+; comparison of the activity with A23187 and carbonyl cyanide p-trifluoromethoxyphenylhydrazone indicated that the prostaglandin B1 oligomers were functioning as ionophores and the release of Ca2+ was not caused by an uncoupling of oxidative phosphorylation. The oligomers caused a major decrease in the membrane potential but only when the mitochondria were preloaded with exogenous Ca2+, and even then, the Ca2+ efflux was completed before the membrane potential decreased to less than 90 mV. The oligomeric molecules were able to form supramolecular aggregates in the presence of Ca2+ as detected by light scattering. They extracted Ca2+ into an organic phase, and translocated Ca2+ from one aqueous domain to another across an organic barrier; K+ and Na+ modulated these processes. The prostaglandin B1 derivatives also translocated Rb+ from one aqueous phase to another across an organic barrier when Ca2+ was translocated.     

Cholecystokinin-stimulated pepsinogen secretion and cholecystokinin receptors on gastric chief cells in guinea pigs

We investigated cholecystokinin (CCK) receptors on isolated gastric chief cells from guinea pig. CCK stimulated pepsinogen secretion from chief cells at the same efficacy as that induced by carbamylcholine. Binding of 125I-labeled CCK-33 (125I-CCK) to chief cells was temperature-dependent, and was saturable and reversible at 37 degrees C. Hofstee plots of the ability of CCK-8 to inhibit binding of 125I-CCK showed a linear regression line, suggesting that CCK receptors possessed one binding site. The dissociation constant of the binding site was calculated to be 3.8 x 10(-10) M. The dose-response curve of CCK for pepsinogen secretion was superimposed on that for the binding to its receptors. These results indicated that gastric chief cells from the guinea pig possess CCK receptors that relate closely to the action of CCK involved in pepsinogen secretion.