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Biomedical subjects

F Hofmann

Publications and source records attributed to F Hofmann.

At least 361 records · Page 20Linked to original sources
PubMed1982

Injection of subunits of cyclic AMP-dependent protein kinase into cardiac myocytes modulates Ca2+ current.

beta-Adrenergic stimulation of the heart is thought to increase cardiac muscle contractility by activation of cyclic AMP-dependent protein kinase and concomitant increase in the phosphorylation of certain proteins (for refs see refs 1-6). Electrophysiological studies have shown that the stimulation of cardiac beta-adrenoreceptors, the external application of cyclic AMP or its analogues to Purkinje fibres, or the injection of cyclic AMP into single myocytes can increase the slow inward current (Isi) during the plateau phase of the action potential (AP). In heart muscle this current is mainly carried by Ca2+ (refs 10, 11) and it has been suggested that cyclic AMP-dependent phosphorylation of some component of the calcium channel increases the amount of Ca2+ which enters the cell during depolarization. We have investigated this hypothesis by examining the electrical responses of isolated guinea pig ventricular myocytes to pressure injections of subunits of the cyclic AMP-dependent protein kinase. We report here that injection of the catalytic subunit (C) resulted in a lengthening of the action potential duration (APD) and an increase in the height of the plateau as well as the amplitude of Isi. By contrast, the injection of regulatory subunit (R) shortened the APD of fast and slow response APs, an effect which was reversed by adrenaline.

Action Potentials↗
PubMed1981

Purification of a soluble, sodium-nitroprusside-stimulated guanylate cyclase from bovine lung.

A soluble, sodium-nitroprusside-stimulated guanylate cyclase as been purified from bovine lung by DEAE-cellulose chromatography, ammonium sulfate precipitation, chromatography on Blue Sepharose CL-6B and preparative gel electrophoresis. Apparent homogeneity was obtained after at least 7000-fold purification with a yield of 3%. A single stained band (Mr 72000) was observed after gel electrophoresis in the presence of sodium dodecyl sulfate. The purified enzyme migrated as one band also under non-denaturing conditions in acrylamide gels (5-12%). The mobility of this band corresponded to an Mr of 145000. The enzyme sedimented on sucrose gradients with an S20, w of 7.0 S. Gel filtration yielded a Stokes' radius of 4.6 nm. These data suggest that the enzyme has an Mr of approximately 150000 and consists of two, presumably identical, subunits of Mr 72000. Sodium nitroprusside stimulated the purified enzyme 15-fold and 140-fold to specific activities of 8.5 and 15.7 mumol of cGMP formed min-1 mg-1 in the presence of Mn2+ and Mg2+, respectively. Formation of cGMP was proportional to the incubation time and to the amount of enzyme added. The stimulatory effect of sodium nitroprusside was half-maximal at about 2 microM, was observed immediately after addition and could be reversed either by dilution or by removal of sodium nitroprusside on a Sephadex G-25 column. The purified enzyme in the absence of catalase was stimulated by sodium nitroprusside, N-methyl-N'-nitro-N-nitrosoguanidine and 3-morpholino-sydnonimine and in the presence of catalase by sodium nitrite and sodium azide. In the presence of Mn2+ and sodium nitroprusside, the purified enzyme catalyzed the formation of cAMP from ATP at a rate of 0.6 mumol min-1 mg-1.

Animals↗
PubMed1981

Enzyme immunoassay and radioimmunoassay for plasma renin activity. I. Comparison of the methods.

Sensitive and specific enzyme and radioimmunoassays have been developed for the determination of renin activity. These methods are based upon the determination of angiotensin I generated by endogenous renin and angiotensinogen. An antibody trapping technique was used, while the addition of chemicals to the plasma, used until now as inhibitors for converting enzyme and angiotensinases, was eliminated. The angiotensin I was labelled with horseradish peroxidase for enzyme immunoassay and with iodine-125 for radioimmunoassay. Antibody bound and free labelled antigen were separated from each other by a second antibody polyethyleneglycol method (enzyme immunoassay) and by charcoal-dextran adsorption (radioimmunoassay). The values of renin activity in human plasma determined by enzyme immunoassay correlated well with those obtained by radioimmunoassay.

Adult↗
PubMed1980

Comparison of phosphorylation of ribosomal proteins from HeLa and Krebs II ascites-tumour cells by cyclic AMP-dependent and cyclic GMP-dependent protein kinases.

Phosphorylation of eukaryotic ribosomal proteins in vitro by essentially homogeneous preparations of cyclic AMP-dependent protein kinase catalytic subunit and cyclic GMP-dependent protein kinase was compared. Each protein kinase was added at a concentration of 30nM. Ribosomal proteins were identified by two-dimensional gel electrophoresis. Almost identical results were obtained when ribosomal subunits from HeLa or ascites-tumour cells were used. About 50-60% of the total radioactive phosphate incorporated into small-subunit ribosomal proteins by either kinase was associated with protein S6. In 90 min between 0.7 and 1.0 mol of phosphate/mol of protein S6 was incorporated by the catalytic subunit of cyclic AMP-dependent protein kinase. Of the other proteins, S3 and S7 from the small subunit and proteins L6, L18, L19 and L35 from the large subunit were predominantly phosphorylated by the cyclic AMP-dependent enzyme. Between 0.1 and 0.2 mol of phosphate was incorporated/mol of these phosphorylated proteins. With the exception of protein S7, the same proteins were also major substrates for the cyclic GMP-dependent protein kinase. Time courses of the phosphorylation of individual proteins from the small and large ribosomal subunits in the presence of either protein kinase suggested four types of phosphorylation reactions: (1) proteins S2, S10 and L5 were preferably phosphorylated by the cyclic GMP-dependent protein kinase; (2) proteins S3 and L6 were phosphorylated at very similar rates by either kinase; (3) proteins S7 and L29 were almost exclusively phosphorylated by the cyclic AMP-dependent protein kinase; (4) protein S6 and most of the other proteins were phosphorylated about two or three times faster by the cyclic AMP-dependent than by the cyclic GMP-dependent enzyme.

Animals↗
PubMed1980

Purification of myosin light chain kinase from bovine cardiac muscle.

Myosin light chain kinase was purified > 100,000-fold to apparent homogeneity with a yield of 10% from bovine cardiac muscle. Sodium dodecyl sulfate gels of the purified kinase showed one stained band corresponding to a Mr of 94,000. The enzyme was activated > 10-fold in the presence of Ca2+ (apparent Ka = 0.6-1.2 microM) and calmodulin (apparent Ka = 3-5 nM). The purified enzyme had a specific activity of 20-30 mumol of phosphate transferred per min per mg from ATP to cardiac myosin light chain 2. One mole of phosphate was incorporated per 94,000 g of the kinase in the presence of Ca2+ and calmodulin or of cyclic AMP-dependent protein kinase or of both additions. In addition to myosin light chain kinase, a calmodulin-binding protein of unknown function was purified from bovine cardiac muscle. This protein had a Mr of 85,000, was composed of two dissimilar subunits (Mr of 61,000 and 15,000), and competed with myosin light chain kinase for calmodulin. The protein appears to be closely related to the calmodulin-binding protein I purified from brain.

Animals↗
PubMed1980

[Action principles of hormones and neurotransmitters (author's transl)].

Membrane-bound receptors for hormones and neurotransmitters can be coupled to other membrane components which generate intracellular signals triggering the cellular response to the hormonal stimulus. For various hormonal factors, the occurrence of receptor subclasses has been established which are bound to different cellular signal-generating systems. Whereas one group of receptors (e.g., beta-adrenergic ones) is linked to adenylate cyclase in a stimulatory manner, other receptors (e.g., alpha 2-adrenergic ones) are linked to this enzyme in an inhibitory manner, and a third group (e.g., alpha 1-adrenergic receptors) is linked to changes in phosphatidylinositol metabolism, calcium distribution and cyclic GMP metabolism. It is not clear whether one given receptor can be linked only to one signal-generating system or whether one type of receptor can be linked to two different signal systems in one cell.

Animals↗
PubMed1980

[Regulation of cellular functions of protein phosphorylation (author's transl)].

The biochemical mechanisms involved in the regulation of cellular functions by intracellular signals, such as calcium, cyclic AMP and cyclic GMP, are described briefly. Each cyclic nucleotide regulated diverse cellular functions by activating a specific protein kinase. Calcium, on the other hand, has several intracellular receptors, i. e., troponin-C, calmodulin and others, which may be present together in the same cell. In the presence of calcium, calmodulin activates a variety of enzymes including protein kinases, phosphorylase kinase and myosin light chain kinase. The specificity of hormonal effects in different tissues depends not only on the presence of the specific intracellular receptor system for each intracellular signal but also on the presence of specific isoenzymic forms of important regulatory enzymes, whose activity may or may not be regulated by phosphorylation and dephosphorylation.

Calcium↗
PubMed1979

Comparative metabolic studies on liver sinusoidal cells and different types of macrophages.

Sinusoidal cells of rat liver, rat peritoneal macrophages and rabbit alveolar macrophages were checked for their viability and compared with regard to cell weight, protein and DNA content. Glycogen was virtually absent from sinusoidal cells and peritoneal macrophages; alveolar macrophages contained glycogen whose level increased after activation by Freund's adjuvant and decreased during phagocytosis in the absence of glucose. Of the different nucleotides assayed, UDPglucose levels were low in the nonglycogen-forming cells, but quite high in alveolar macrophages. The capacity to metabolize galactose is much smaller in all cell types investigated than in hepatocytes.

Animals↗