Biomedical subjects

G Liljeqvist

Publications and source records attributed to G Liljeqvist.

10 recordsLinked to original sources

PubMed1986

Pitfalls in the assay of cyclic AMP-dependent protein kinase activity in microsacs from Torpedo marmorata.

Endogenous phosphorylation of the nicotinic acetylcholine receptor (nAChR) in microsacs from Torpedo marmorata was found to be affected by several reagents commonly used in the preparation of cyclic AMP (cAMP)-dependent protein kinases and in its activity determination. The presence of a Na+,K+-ATPase inhibitor is essential to avoid a rapid depletion of ATP, even when a membrane fraction highly enriched in the nAChR is used. The presence of the thiol reducing agent dithiothreitol was found to abolish the cAMP dependence of nAChR phosphorylation, whereas the less potent reagent 2-mercaptoethanol did not affect the assay. Concentrations in the millimolar range of the chelators EDTA and EGTA were found to inhibit nAChR phosphorylation effectively. This inhibition was not due to a withdrawal of Ca2+ by the chelators, but rather to a reversible inhibition by the Mg2+ complexes. These observations may explain some of the discrepancies found in the literature concerning endogenous and exogenous nAChR phosphorylation.

Animals↗

PubMed1983

Extraction of peripheral proteins from nicotinic acetylcholine receptor-enriched membranes.

The solubilisation of membrane proteins from nicotinic acetylcholine receptor-enriched membranes from the electric organ of Torpedo marmorata was studied. Chaotropic ions were shown to be ineffective in extracting peripheral proteins from these membranes. Two different anhydrides, 2, 3-dimethylmaleic and 3,4,5,6-tetrahydrophthalic anhydride, released certain peripheral membrane proteins but not the integral receptor protein. Treatment of membranes containing greater than 3 nmol alpha-bungarotoxin binding sites per mg protein with anhydride resulted in a 43 kDa polypeptide as the major constituent of the solubilised material. The nature of the 43 kDa polypeptide is discussed. Gentle anhydride treatment did not change the alpha-bungarotoxin and carbamoylcholine binding properties of the receptor.

Animals↗

PubMed1982

Hemoglobins, XLVIIII. The primary structure of a monomeric hemoglobin from the hagfish, Myxine glutinosa L.: evolutionary aspects and comparative studies of the function with special reference to the heme linkage.

Hagfish hemoglobin has three main components, one of which is Hb III. It is monomeric and consists of 148 amino acid residues (M = 17 350). Its complete primary structure, previously published, is discussed here. The proximal amino acid (F8) of the heme linkage is histidine as always in the hemoglobins, but the regularly expected distal histidine E7 is substituted by glutamine. This substitution, leading to a new kind of heme linkage, has hitherto only been demonstrated in opossum hemoglobin. It is suggested that E7, Gln, is directed out of the heme pocket, and that the adjacent Ell, Ile, is directed toward the inside of the pocket, giving the distal heme contact instead of histidine. Myxine Hb III has an additional tail of 9 amino acid residues at its N-terminal end, as has the hemoglobin of Lampetra fluviatilis. The genetic codes of Myxine and Lampetra hemoglobins show 117 differences, in spite of many morphological resemblances between hagfish and lamprey. Their primary hemoglobin structures show differences substantial enough to be compatible with the divergence of the two families some 400-500 million years ago.

Amino Acid Sequence↗

PubMed1979

[Hemoglobins. XXVII. The amino acid sequence of hemoglobin III from Myxine glutinosa L. A new hemecomplex: E7 glutamine, E11 isoleucine].

The sequence analysis of the main component, "HbIII", of the hemoglobins from the hagfish (Myxine glutinosa L.) is described. The hagfish belongs to the Cyclostomata, the most primitive class of the vertebrates. The hagfish hemoglobin displays a great heterogeneity, as described earlier. It consists of several monomeric hemoglobins. The globin of HbIII was isolated and used for the sequence analysis. The tryptic peptides as well as the cyanogen bromide and the BNPS-skatol fragments were separated. The sequences of the peptides were determined automatically by the help of a sequenator. Compared with other hitherto analyzed vertebral hemoglobins, also including other Cyclostomata, the primary structure of "HbIII" differs by more than 50%. The differences are so many that one can refer the Myxine hemoglobin neither as an alpha- nor as a beta-chain (of the tetrameric hemoglobins). The hagfish hemoglobin like other Cyclostomata has an additional segment of 9 residues at the amino terminus end compared with the mammalian hemoglobins. In the F-helix there is an insertion of 3 amino acid residues and in the interhelical gap, GH, there is a deletion of 9 residues. The substitutions of the residues forming the heme complex are of special interest. The distal histidine, E7, is substituted for glutamine. The proximal histidine, F8, is invariable. The valine E11 is substituted by isoleucine and the leucine FG3 by phenylalanine. These positions are involved in the contact with the heme group. This complex has never been described before.

Amino Acid Sequence↗

PubMed1972