Biomedical subjects

Krzysztof Krawiec

Publications and source records attributed to Krzysztof Krawiec.

4 recordsLinked to original sources

PubMed2005

Visual learning by coevolutionary feature synthesis.

In this paper, a novel genetically inspired visual learning method is proposed. Given the training raster images, this general approach induces a sophisticated feature-based recognition system. It employs the paradigm of cooperative coevolution to handle the computational difficulty of this task. To represent the feature extraction agents, the linear genetic programming is used. The paper describes the learning algorithm and provides a firm rationale for its design. Different architectures of recognition systems are considered that employ the proposed feature synthesis method. An extensive experimental evaluation on the demanding real-world task of object recognition in synthetic aperture radar (SAR) imagery shows the ability of the proposed approach to attain high recognition performance in different operating conditions.

Algorithms↗

PubMed2003

Inorganic tripolyphosphate (PPP(i)) as a phosphate donor for human deoxyribonucleoside kinases.

Inorganic tripolyphosphate (PPP(i)) and pyrophosphate (PP(i)) were examined as potential phosphate donors for human deoxynucleoside kinase (dCK), deoxyguanosine kinase (dGK), cytosolic thymidine kinase (TK1), mitochondrial TK2, and the deoxynucleoside kinase (dNK) from Drosophila melanogaster. PPP(i) proved to be a good phosphate donor for dGK, as well as for dCK with dCyd, but not dAdo, as acceptor substrate, illustrating also the dependence of donor properties on acceptor. Products of phosphorylation were shown to be 5(')-phosphates. In striking contrast to ATP, the phosphorylation reaction follows strict Michaelis-Menten kinetics, with K(m) values of 74 and 92 microM for dCK and dGK, respectively, and V(max) values 40-50% that for ATP. With the other three enzymes, as well as for dCK with dAdo as acceptor, no, or only low levels (</=1% of that for ATP) of activity were observed. PP(i) was inactive (<0.1%) as a phosphate donor with all enzymes, but was a competitive inhibitor vs ATP, as was PPP(i) in systems with no or low donor activity. This is the first report on inorganic tripolyphosphate as a phosphate donor for nucleoside kinases, in particular human deoxyribonucleoside kinases.

Adenosine Triphosphate↗

PubMed2003

Striking ability of adenosine-2'(3')-deoxy-3'(2')-triphosphates and related analogues to replace ATP as phosphate donor for all four human, and the Drosophila melanogaster, deoxyribonucleoside kinases.

In extension of an earlier report, six non-conventional analogues of ATP, three adenosine-2'-triphosphates (3'-deoxy, 3'-deoxy-3'-fluoro- and 3'-deoxy-3'-fluoroxylo-), and three adenosine-3'-triphosphates (2'-deoxy-, 2'-deoxy-2'-fluoro- and 2'-deoxy-2'-fluoroara-), were compared with ATP as potential phosphate donors for human deoxycytidine kinase (dCK), cytosolic thymidine kinase (TK1), mitochondrial TK2, deoxyguanosine kinase (dGK), and the deoxyribonucleoside kinase (dNK) from Drosophila melanogaster. With one group of enzymes, comprising TK1, TK2, dNK and dCK (with dAdo as acceptor), only 3'-deoxyadenosine-2'-triphosphate was an effective donor (5-60% that for ATP), and the other five analogues much less so, or inactive. With a second set, including dCK (dCyd, but not dAdo, as acceptor) and dGK (dGuo as acceptor), known to share high sequence similarity (approximately 45% sequence identity), all six analogues were good to excellent donors (13-119% that for ATP). With dCK and ATP1, products were shown to be 5'-phosphates. With dCK, donor properties of the analogues were dependent on the nature of the acceptor, as with natural 5'-triphosphate donors. With dCK (dCyd as acceptor), Km and Vmax for the two 2'(3')-deoxyadenosine-3'(2')-triphosphates are similar to those for ATP. With dGK, Km values are higher than for ATP, while Vmax values are comparable. Kinetic studies further demonstrated Michaelis-Menten (non-cooperative) or cooperative kinetics, dependent on the enzyme employed and the nature of the donor. The physiological significance, if any, of the foregoing remains to be elucidated. The overall results are, on the other hand, highly relevant to studies on the modes of interaction of nucleoside kinases with donors and acceptors; and, in particular, to interpretations of the recently reported crystal structures of dGK with bound ATP, of dNK with bound dCyd, and associated modeling studies.

Animals↗

PubMedDate not supplied

Ability of adenosine-2'(3')-deoxy-3'(2')-triphosphates and related analogues to replace ATP as phosphate donor for all human and Drosphila melanogaster deoxyribonucleoside kinases.

Six non-conventional adenosine-2'- and 3'-triphosphate analogues of ATP were tested as potential phosphate donors for all four human, and D. melanogaster, deoxyribonucleoside kinases. With dCK (only dAdo as acceptor), TK1, TK2 and dNK only 3'-deoxyadenosine-2'-triphosphate was an effective donor (5-60% that for ATP). With dCK (dCyd as acceptor) and dGK (dGuo as acceptor), sharing 45% sequence identity, donor activities ranged from 13 to 119% that for ATP. Products were 5'-phosphates. In some instances, kinetics are dependent on the nature of the acceptor, and donor and acceptors properties are mutually interdependent. Results are highly relevant to studies on the modes of interaction with the enzymes, and to interpretations of reported crystal structures of dCK and dNK with bound ligands.

Adenosine Triphosphate↗