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Biomedical subjects

J F Koster

Publications and source records attributed to J F Koster.

At least 109 records · Page 6Linked to original sources
PubMed1980

The role of Ca2+ and cyclic AMP in the phosphorylation of rat-liver soluble proteins by endogenous protein kinases.

Rat liver soluble proteins were phosphorylated by endogenous protein kinase with [gamma-32P]ATP. Proteins were separated in dodecyl sulphate slab gels and detected with the aid of autoradiography. The relative role of cAMP-dependent, cAMP-independent and Ca2+-activated protein kinases in the phosphorylation of soluble proteins was investigated. Heat-stable inhibitor of cAMP-dependent protein kinase inhibits nearly completed the phosphorylation of seven proteins, including L-type pyruvate kinase. The phosphorylation of eight proteins is not influenced by protein kinase inhibitor. The phosphorylation of six proteins, including phosphorylase, is partially inhibited by protein kinase inhibitor. These results indicate that phosphoproteins of rat liver can be subdivided into three groups: phosphoproteins that are phosphorylated by (a) cAMP-dependent protein kinase or (b) cAMP-independent protein kinase; (c) phosphoproteins in which both cAMP-dependent and cAMP-independent protein kinase play a role in the phosphorylation. The relative phosphorylation rate of substrates for cAMP-dependent protein kinase is about 15-fold the phosphorylation rate of substrates for cAMP-independent protein kinase. The Km for ATP of cAMP-dependent protein kinase and phosphorylase kinase is 8 microM and 38 microM, respectively. Ca2+ in the micromolare range stimulates the phosphorylation of (a) phosphorylase, (b) a protein with molecular weight of 130 000 and (c) a protein with molecular weight of 15 000. The phosphate incorporation into a protein with molecular weight of 115 000 is inhibited by Ca2+. Phosphorylation of phosphorylase and the 15 000-Mr protein in the presence of 100 microM Ca2+ could be completely inhibited by trifluoperazine. It can be concluded that calmodulin is involved in the phosphorylation of at least two soluble proteins. No evidence for Ca2+-stimulated phosphorylation of subunits of glycolytic or gluconeogenic enzymes, including pyruvate kinase, was found. This indicates that it is unlikely that direct phosphorylation by Ca2+-dependent protein kinases is involved in the stimulation of gluconeogenesis by hormones that act through a cAMP-independent, Ca2+-dependent mechanism.

Adenosine Triphosphate↗
PubMed1979

McArdle's disease: a study on the molecular basis of two different etiologies of myophosphorylase deficiency.

Three patients with myophosphorylase deficiency were investigated. Two had no detectable activity, while one had 1% residual activity. The patient with 1% residual activity had 40% of the normal amount of myophosphorylase protein. No myophosphorylase protein could be detected in the other two cases. A precipitin band in the Ouchterlony double immunodiffusion test was not present in any case. This study showed that modifying the normal enzyme (without changing the molecular weight) changed the immunoprecipitin activity of the phosphorylase protein. Therefore, immunoprecipitation is not a valid technique for differentiation of the variants of myophosphorylase deficiency, and another method, for example SDS-electrophoresis, should be applied.

Electrophoresis, Polyacrylamide Gel↗
PubMed1979

Binding of unmodified low-density lipoproteins to human fibroblasts. An investigation by immunoelectron microscopy.

The bindinf of unmodified low density lipoproteins to the plasma membrane of fibroblasts was studied at the ultrastructural level. The bound low density lipoprotein was visualized by an indirect immunoperoxidase technique, with the use of an antiserum against apoprotein B. Immunoreactive regions representing bound apoprotein B were found on the plasma membrane, in indented regions with a diameter of 0.15--0.30 micrometer and a fuzzy coat on the cytoplasmic side. Fibroblasts from a patient homozygous for hyperlipoproteinaemia type IIa showed no immunoreactive material in the indented regions. The specific 125I-labelled low density lipoprotein binding to these homozygous fibroblasts was 7% compared to control fibroblasts.

Cell Aggregation↗
PubMed1979

Biochemical studies in Hermansky-Pudlak syndrome.

In order to find the basic defect in the Hermansky-Pudlak Syndrome (HPS), biochemical studies of platelets and leucocytes were undertaken. Glutathione levels of platelets were normal and regeneration of GSH similar to controls occurred after incubation with diamide (a specific agent for GSH oxidation). Phospholipid and fatty acid composition of HPS platelets was normal. The amount of peroxides found in platelet membranes was not elevated. A subnormal aggregation with arachidonic acid could be obtained in PRP using a high concentration of arachidonic acid (2 mM), but normal malondialdehyde levels were measured, suggesting a normal prostaglandin synthesis in HPS platelets. Glutathion peroxidase and p-phenylenediamide-mediated peroxidase (PPD-peroxidase) were normal in leucocytes of 1 HPS patient. Lysosomal enzymes as far as investigated were normal.

Albinism↗
PubMed1979

Infantile and adult-onset acid maltase deficiency occurring in the same family.

A 16-week-old girl died from the infantile form of acid maltase deficiency (Pompe disease, acid alpha-glucosidase deficiency). Her paternal grandfather was well until the age of 53 years, when he started to suffer from the adult-onset form of the same enzyme deficiency. This observation suggests that the infantile and adult-onset forms of acid maltase deficiency are genetically related.

Age Factors↗
PubMed1978

Biochemical, immunological, and cell genetic studies in glycogenosis type II.

Fibroblasts from patients with the adult, juvenile, and infantile form of glycogenosis type II (Pompe disease) were cultured under standardized conditions, and the activity of acid alpha-glucosidase (E.C.3.2.1.20) towards glycogen, maltose, and 4-methylumbelliferyl-alpha-D-glucopyranoside was measured. Glycogen levels in muscle biopsies and in cultured fibroblasts from patients were determined. Residual enzyme activities varying from 7%-22% were detected in fibroblasts from patients with the adult form but not from patients with the infantile form of glycogenosis II. An inverse correlation was found between the severity of the clinical manifestation and the degree of residual enzyme activity in the fibroblasts. The kinetic and electrophoretic properties of acid alpha-glucosidase in fibroblasts from the adult patients and from control individuals were similar. Immunological studies suggested that the decrease of acid alpha-glucosidase activity is caused by a mutation that affects the production or degradation of the enzyme rather than its catalytic activity. Complementation studies were carried out by fusing fibroblasts from patients with the adult, juvenile, and infantile form of glycogenosis II, but neither conventional assays on multikaryons nor enzyme assays on single binuclear heterokaryons gave any evidence for genetic heterogeneity among these forms.

Adolescent↗
PubMed1977

Influence of the rebox state of glutathione upon pyruvate kinase in the intact erythrocyte.

1. In isolated erythrocytes the ratio of reduced to oxidized glutathione was modified by the addition of diazinedicarboxylic acid bis-dimethylamide (diamide). Incubation of erythrocytes, with a decreased GSH/GSSG ratio, resulted in an increase in [S]0.5 of pyruvate kinase of phosphoenolpyruvate as measured in haemolysates. We presume this increase to be due to oxidation of the enzyme. 2. The apparent affinity of pyruvate kinase for phosphoenolpyruvate returned to normal when the GSSG formed was reduced to GSH intracellularly. Oxidation of pyruvate kinase could also be reversed by incubation of haemolysates with reducing agents such as 2-mercaptoethanol or dithioerythritol. 3. Intracellular oxidation of pyruvate kinase caused no significant changes in the Hill coefficient (n) or Vmax of the enzyme. However, the heat stability of the oxidized enzyme was lower than normal. Lability increased with increasing oxidation of the enzyme. 4. The possible role of oxidation processes in pyruvate kinase deficiency is discussed. It is concluded that not only 'in vitro' but also in the intact erythrocyte, pyruvate kinase is sensitive to oxidizing agents and intracellular redox state. However, that a decreased GSH/GSSG ratio can be a single cause of acquired pyruvate kinase deficiency seems highly improbable.

Diamide↗
PubMed1977

Some properties of human liver acid alpha-glucosidase.

1. Albumin activates human liver acid alpha-glucosidase (alpha-D-glucoside hydrolase, EC 3.2.1.20). From the Arrhenius plot, pH-dependence and Lineweaver-Burk plots it can be concluded that this activation is not only due to stabilisation of the enzyme, but also influences the enzymatic activity. It is proposed that for optimal functioning human liver acid alpha-glucosidase needs a protein environment. 2. Glycogen has a competitive inhibitory effect on the hydrolysis of 4-methylumbelliferyl-alpha-D-glucopyranoside, in contrast to maltose which exhibits a non-competitive type of inhibition. It is concluded that two catalytic sites exist, one for glycogen and one for maltose, while both sites influence each other. With glycogen as substrate a break in the Arrhenius plot is found. This is not the case when maltose is used as substrate. 3. The effect of antibody raised against human liver acid alpha-glucosidase on the activity of human liver acid alpha-glucosidase is studied. No corss-reacting material could be demonstrated in the liver of a patient with glycogen storage disease Type II (M. Pompe, acid alpha-glucosidase deficiency).

Antigen-Antibody Reactions↗