PubMed Health⌕ Search

Biomedical subjects

S Erickson-Viitanen

Publications and source records attributed to S Erickson-Viitanen.

48 records · Page 3Linked to original sources
PubMed1985

Purification and properties of rabbit liver cathepsin M and cathepsin B.

Cathepsins M and B from rabbit liver lysosomes were separated by chromatography on Ultrogel AcA34 at low ionic strength and purified to homogeneity, and their catalytic and molecular properties were compared. Cathepsin M was relatively inactive with synthetic peptide substrates. Thus, it hydrolyzed benzoyl arginine naphthylamide at only one-fifth the rate observed with cathepsin B, and no activity was detected with Gly-Phe naphthylamide which is a relatively good substrate for cathepsin B. On the other hand, cathepsin M exhibited a preference for protein substrates. It was more active than cathepsin B in catalyzing the inactivation of the following enzymes: rabbit muscle or liver fructose-1,6-bisphosphate aldolases, rabbit liver fructose-1,6-bisphosphatase and pyruvate kinase, yeast glucose-6-phosphate dehydrogenase, and rabbit muscle glyceraldehyde-3-phosphate dehydrogenase. With glucagon as substrate, both enzymes showed similar peptidyl dipeptidase activities with some minor differences in peptide bond specificity. Cathepsins M and B are similar in size, with apparent molecular weights of 30,200 for cathepsin M and 28,800 for cathepsin B, and in amino acid composition and carbohydrate content. Each contains approximately 2-3 equivalents/mol glucosamine, 3 equivalents/mol mannose, and no fucose or galactosamine. They also show similar microheterogeneity in sodium dodecylsulfate-gel electrophoresis and isoelectric focusing; this microheterogeneity is probably related to differences in glycosylation. Extensive homology in primary structure for the two proteins was indicated by the similar patterns of peptides formed on digestion with trypsin.

Amino Acids↗
PubMed1984

Evidence for functional hexokinase compartmentation in rat skeletal muscle mitochondria.

Further studies of mitochondrially bound hexokinase have been carried out in order to elucidate the mechanism first proposed to increase efficiency of oxidative phosphorylation by the acceptor effect (Bessman, S. P. (1954) in Fat Metabolism (Najjar, V., ed) pp. 133-137, Johns Hopkins Press, Baltimore). During isolation of mitochondria, Mg2+ caused increased quantities of hexokinase to be bound or retained. This effect is concentration-dependent, saturable, and cannot be explained by Mg2+-linked activation or stabilization. Rebinding of hexokinase to isolated mitochondria also shows a similar dependence on Mg2+. When added to a homogenate made without it, Mg2+ could not bind the same amount of hexokinase to the mitochondria as could be observed when Mg2+ had been included in the homogenizing medium from the start. Using mitochondria prepared with Mg2+ in order to bind hexokinase to the largest extent possible, we have demonstrated that as in the case of mitochondrial creatine phosphokinase, a compartment exists that permits more efficient production of glucose 6-phosphate during mitochondrial respiration--the hexokinase acceptor effect. This effect probably results from a favorable positioning of the active site of hexokinase, perhaps within the intermembrane space, providing a diffusion-favorable situation. Thus, newly synthesized ATP transported through the inner membrane supplies substrate to hexokinase with greater efficiency than that of ATP which must pass through the outer membrane by diffusion from the medium. These observations lend support to proposals that in vivo modulation of the soluble particulate distribution of hexokinase by hormones or by metabolites may be physiologically necessary and important.

Adenine Nucleotides↗
PubMed1984

Thymosin beta 11: a peptide from trout liver homologous to thymosin beta 4.

A peptide containing 41 amino acid residues has been isolated from trout liver and identified as a member of the beta-thymosin family. Sequence analysis shows it to be 78% homologous to thymosin beta 4, which is the peptide present in the thymus and other tissues of higher vertebrates, including, as reported here, livers of a species of reptile. Thymosin beta 11 appears to replace the more prevalent thymosin beta 4 in at least two species of bony fish, and represents the sixth structurally characterized member of this widely distributed family of peptides.

Amino Acid Sequence↗
PubMed1983

Thymosin beta arg10, a major variant of thymosin beta 10 in rabbit tissues.

Two homologous peptides, designated thymosin beta 4 and thymosin beta 10, respectively, have been shown to be widely distributed in mammalian cells and tissues (S. Erickson-Viitanen, S. Ruggieri, P. Natalini, and B.L. Horecker (1983) Arch. Biochem. Biophys. 221, 570-576; S. Erickson-Viitanen, S. Ruggieri, P. Natalini, and B.L. Horecker, (1983) Arch. Biochem. Biophys. 225, 407-413). In the rabbit, thymosin beta 4 is replaced by a variant, thymosin beta ala4, that contains alanine in place of serine at the blocked NH2-terminus. It is reported that in rabbit tissues thymosin beta 10 is also replaced by a variant, designated thymosin beta arg10, that contains an additional amino acid, arginine, inserted following lysine-38. The rabbit tissues analyzed also differ from those of other mammals in the relative quantities of thymosin beta ala4 and beta arg10, which are nearly equal, compared to tissues from other mammals where the quantities of thymosin beta 10 are only one-third to one-tenth those of thymosin beta 4.

Amino Acid Sequence↗
PubMed1983

Thymosin beta 10, a new analog of thymosin beta 4 in mammalian tissues.

A new analog of thymosin beta 4 has been isolated from tissues of several mammalian species. This peptide, designated thymosin beta 10, is composed of 42 amino acid residues and shows 75% sequence homology with thymosin beta 4. It occurs together with thymoxin beta 4 in a variety of tissues including spleen, liver, and thymus and also in several cultured cell lines. In the spleen of rat, mouse, cat, and man, the new peptide accounts for approximately 0.02% by weight of the total protein. In the calf it is replaced by another homologous peptide, designated thymosin beta 9, whose structure has been reported.

Amino Acid Sequence↗
PubMed1983

Distribution of thymosin beta 4 in vertebrate classes.

A peptide containing 43 amino acid residues, rich in glutamic acid and lysine, was originally isolated from calf thymus and designated thymosin beta 4 [T.L.K. Low, S. -K. Hu, and A. L. Goldstein (1981) Proc. Nat. Acad. Sci. USA 78, 1162-1166]. However, thymosin beta 4 was also shown to be present in other tissues of rats and mice, with highest concentrations in spleen and peritoneal macrophages [E. Hannappel, G.-J. Xu, J. Morgan, J. Hempstead, and B.L. Horecker (1982), Proc. Nat. Acad. Sci. USA 79, 2172-2175]. We have now identified the same peptide in tissues of other mammalian species and other vertebrate classes, including birds and amphibia. Exceptions are the rabbit and bony fish, where thymosin beta 4 is replaced by different peptides, similar in size and in amino acid sequence. None of these peptides was detected in several invertebrates or in the protozoan, Tetrahymena pyriformis. In subcellular fractionation of rat spleen, thymosin beta 4 was recovered in the cytosol.

Animals↗
PubMed1982

Compartmentation of mitochondrial creatine phosphokinase. I. Direct demonstration of compartmentation with the use of labeled precursors.

Mitochondrial creatine kinase was first proposed to act as a functional component in respiratory control in 1966 (Bessman, S. P., and Fonyo, A. (1966) Biochem. Biophys. Res. Commun. 22, 597-602). Since that time, evidence has accumulated to support the theory of a creatine-phosphorylcreatine shuttle mechanism involved in supplying energy for aerobic muscle contraction (Bessman, S. P., and Geiger, P. J. (1981) Science 211, 448-452). To demonstrate directly the interaction between mitochondrial oxidative phosphorylation and that of creatine phosphate synthesis, we have studied the labeling of adenine nucleotides and creatine phosphate with [33P]H3PO4 or [gamma-32P]ATP over a range of adenine nucleotide concentrations incubated with rabbit cardiac and rat skeletal muscle mitochondria. An apparent direct mitochondrial ATP contribution to creatine phosphate synthesis was observed that varied inversely with the total adenine nucleotide present in the reaction system. This reaction of de novo synthesized ATP with creatine phosphokinase prior to equilibration with the total ATP pool was observed regardless of the entry point of electrons from oxidizable substrate into the electron transport chain. This special relation was not observed for added yeast hexokinase in forming glucose 6-phosphate. Mitochondria could not synthesize creatine phosphate in the presence of atractyloside, thus underscoring the requirement for adenine nucleotide translocase-linked transport of ATP prior to reaction with the bound creatine phosphokinase. These studies show that there is coupling or compartmentation of ATP synthesis and transport with creatine phosphate formation in heart and skeletal muscle mitochondria.

Animals↗
PubMed1982

Compartmentation of mitochondrial creatine phosphokinase. II. The importance of the outer mitochondrial membrane for mitochondrial compartmentation.

In order to define further the nature of the apparent close interaction between mitochondrial creatine phosphokinase and oxidative phosphorylation (Erickson-Viitanen, S., Viitanen, P., Geiger, P. J., Yang, W. C. T., and Bessman, S. P. (1982) J. Biol. Chem. 257, 14395-14404), rabbit heart and rat skeletal muscle mitochondria prepared by gentle mechanical homogenization were compared with preparations isolated after tryptic digestion of tissues, a method which has been reported to yield superior mitochondria (Reichert, M., Schaller, H., Kung, W., and Gerber, G. (1978) Acta Biol. Med. Germ. 37, 1167-1176). The ability of de novo synthesized and exported mitochondrial ATP to interact with creatine phosphokinase prior to total mixing of the ATP pool, which we consider to be evidence of compartmentation, could not be demonstrated with mitochondria prepared via the trypsin procedure. Mitochondria from rabbit cardiac muscle treated with digitonin synthesized ATP and creatine phosphate, but failed to show apparent compartmentation of creatine phosphokinase. Km values for ATP were compared for four conditions: 1) respiring, digitonin-treated rabbit heart mitochondria, 2) atractyloside-inhibited, digitonin-treated rabbit heart mitochondria supplied with a pyruvate kinase-phosphoenolpyruvate regenerating system, 3) respiring rabbit heart mitochondria, 4) atractyloside-inhibited rabbit heart mitochondria supplied with an ATP regenerating system. The observed Km values for ATP for conditions 1, 2, and 3 were similar but lower than that for condition 4. These findings suggest that an outer membrane diffusion barrier influences or controls mitochondrial creatine phosphokinase compartmentation.

Animals↗