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P Karlson

Publications and source records attributed to P Karlson.

At least 19 recordsLinked to original sources
PubMed1982

[What are hormones? The term hormone in retrospect and prospect].

Historically, the meaning of the term hormone has changed during the last decades. Morphological studies of secreting cells lead Feyrter to the concept of paracrine action of some hormones. While endocrine regulators are blood-borne, paracrine messengers reach their target cells through the diffusion in the intracellular space. Though it is rather difficult to draw a line between true hormones and hormone-like substances, valid definitions for endocrine and paracrine regulatory systems can be given. The term "hormonal control' should be restricted to endocrine systems. For effectors acting by paracrine mechanisms, the term paramone is proposed in this article.

Animals↗
PubMed1979

[Hormone receptors and hormone action (author's transl)].

All hormones act only on their target tissues. The ability of a tissue to react to a hormone is due to the presence of a receptor in or at the cell. There are two classes of hormone receptors: those bound to the membrane and those present in the cytosol. Peptide hormones generally act through membrane receptors. The interaction of a hormone with its receptors leads to an activation of the adenylate cyclase and the production of cyclo-AMP, the second messenger. In cases where several hormones act on the same tissue (example: adipose tissue) they must interact with their specific receptors, but presumably with the same adenylate cyclase. This interaction is discussed. The receptors for steroid hormones are not membrane-bound, but present in the cytosol. They are specific proteins which bind the hormone rather tightly. This results in a change in protein conformation, sometimes accompanied by a dimerization; the modified receptor is then transferred to the cell nucleus where it stimulates transcription. The control mechanisms of transcription are discussed; the most probable mode of action is removal of a repressor or repressor-like component from chromatin which results in deinhibition of transcription. mRNA is then produced and translated into protein. Post-transcriptional controls have been postulated, but never unequivocally demonstrated.

Adenylyl Cyclases↗
PubMed1979

Purification of prophenoloxidase in the haemolymph of Calliphora vicina (R. & D.).

An improved method for the purification of prophenoloxidase is described. The proenzyme was purified 400 fold in homogenous form. The purity was tested by disc-electrophoresis and the molecular weight was found to be 87 000 in comparison to the mobility of marker enzymes, which were run simultaneously in SDS-gel electrophoresis. The proenzyme was denatured at 80 degrees C and maximum conversion into active state was found between 40 and 50 degrees C.

Animals↗
PubMed1978

Ecdysone oxidase: reaction and specificity.

Ecdysone oxidase oxidizes 3-hydroxysteroids of the excysteroid type irreversibly to 3-dehydro derivatives. The hydrogen of the steroid is transferred by the enzyme to oxygen which is reduced to hydrogen peroxide. Ecdysone oxidase is relatively specific for ecdysone and ecdysterone. Apparent Michaelis constants for these two physiological substrates are 98 and 31 micron, respectively. Cholesterol oxidase and 3alpha-hydroxysteroid and 3beta-hydroxysteroid dehydrogenases which catalyze similar reactions are unable to oxidize ecdysteroids.

3-Hydroxysteroid Dehydrogenases↗
PubMed1975

[Topochemistry of hormone action].

The site of hormone action is the cells of target tissues. Now that ultrastructural research has revealed the complexity of eukaryotic cells, we must ask which cellular structures are involved. Some hormones act at the cell membrane, mainly via adenylate cyclase and the "second messenger" cAMP. The cytosol and the mitochondria, the main sites of intermediate metabolism and enzyme activity, are apparently not involved, although in the past interaction of hormones with enzymes has been postulated. Most of the steroid hormones act at the level of the cell nucleus, regulating transcription of specific genes and inducing enzymes or other proteins. The mechanisms by means of which this regulation is achieved are not fully understood, but it is likely that derepression is involved. The active agent seems to be a complex of the hormone with a receptor protein.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

Ecdysone Oxidase, an enzyme from the blowfly Calliphora erythrocephala (Meigen).

In the blowfly, the formation of 3-dehydroecdysone from the insect molting hormone ecdysone is catalyzed by an enzyme which carries hydrogen from ecdysone and ecdysterone to oxygen. The enzyme is therefore called "ecdysone oxidase". Two methods are described for the detection of ecdysone oxidase activity, one using a radiolabelled substrate which is separated from the product by thin-layer chromatography after the reaction, and the other using dichloroindophenol, which is discoloured by the redox reaction. The ecdysone oxidase is purified by a factor of 2200 from prepupae of Calliphora erythrocephala using salt precipitation and ion exchange chromatography. The ecdysone oxidase has a Km value for ecdysone of 42muM. The pH optimum is 6.5. The temperature optimum lies at 45 degrees C. The ecdysone oxidase has a molecular weight of 240000.

2,6-Dichloroindophenol↗