Biomedical subjects

P Casellas

Publications and source records attributed to P Casellas.

93 records · Page 6Linked to original sources

PubMed1978

Protein methylation in animal cells. I. Purification and properties of S-adenosyl-L-methionine:protein (arginine) N-methyltransferase from Krebs II ascites cells.

1. A protein methylase which specifically transfers methyl groups from S-adenosyl-L-methionine to arginine residues of histones has been substantially purified from Krebs II ascites cells. The purified enzyme was obtained free of contamination by other protein methyl transferases specific for carboxyl and lysine residues. This latter activity copurified with the present enzyme until advanced stages of purification. 2. The purified enzyme does not require any divalent cation for maximum activity. It is inhibited by ionic strength, N-ethylmaleimide and S-adenosyl-L-homocysteine. It has an apparent molecular weight on gel filtration of approx. 5 . 10(5). A Km value for S-adenosyl-L-methionine of 2.5 . 10(-6) M was determined, while the dissociation constant Ki for S-adenosyl-L-homocysteine, which acts as a competitor, was 1.4 . 10(-6) M.

Animals↗

PubMed1978

Protein methylation in animal cells. II. Inhibition of S-adenosyl-L-methionine:protein(arginine) N-methyltransferase by analogs of S-adenosyl-L-homocysteine.

1. Protein methylase I (S-adenosyl-L-methionine: protein (arginine) N-methyltransferase, EC 2.1.1.23) has recently been purified in our laboratory from Krebs II ascites cells (Casellas, P. and Jeanteur, P. (1978) Biochim. Biophys. Acta 519, 243--254). In order to probe its binding site for S-adenosyl-L-methionine, three series of compounds deriving from the most potent competitive inhibitor, S-adenosyl-L-homocysteine, by specific alterations in each of the three regions of the molecule (amino acid side chain, ribose and adenine) have been tested for inhibitor activity. A competitive type of inhibition was assumed for all of them and demonstrated for five representative ones. The contribution of each of these regions to the binding could therefore be established as follows: (i) Any modification of the side chain results in a drop in affinity of about two orders of magnitude. Adenosine itself remained significantly inhibitory thereby demonstrating that the presence of a side chain was not critical, although important. (ii) The ribose moiety appears to be an essential part of the molecule as the loss of either 2'- or 3'-hydroxyls or their change to arabino configuration resulted in a nearly complete loss of activity. (iii) The amino group at position 6 and the nitrogen atom at position 7 of the adenine ring also play a crucial role although some substitutions can be tolerated. 2. S-Isobutyladenosine was shown to specifically inhibit the methylation of arginine residues as compared to lysine.

Adenosine↗

PubMedDate not supplied

Mutation analysis in the coding sequence of thymidine kinase 1 in breast and colorectal cancer.

We report the first mutational study of thymidine kinase 1 (TK1) performed in human solid tumors. We sequenced cDNAs representing the complete coding region of TK1 in human breast (n=22) and colorectal (n=26) cancer. Codon 106 near the ATP binding site constantly differed (ATG --> GTG; Met --> Val) from the one deposited by Bradshaw and Deininger in the Genbank database (Accession number NM_003258). Silent polymorphisms at codon 11 (CCC --> CCT; Pro --> Pro) and codon 75 (GCG --> GCA; Ala --> Ala) were frequently detected in tumors as well as in normal tissues. In breast cancer the two polymorphisms were observed in 63.6% of the samples analyzed. No significant association could be found between polymorphisms and TK activity. In colorectal cancer the incidence of the two changes was 73.1% and 69.2%, respectively. Interestingly, one colon cancer with high cytosolic TK activity displayed two missense mutations located in and near the putative phosphorylation site by tyrosine kinase (s) (TAT --> CAT; Tyr --> His) and by cAMP-, cGMP-dependent protein kinase (TAC --> TGC; Tyr --> Cys), respectively; adjacent normal mucosa showed no mutation. This may open new avenues that imply TK1 activity in tumor cell proliferation.

Adenosine Triphosphate↗