Search PubMed⌕ Search

Biomedical subjects

M Burke

Publications and source records attributed to M Burke.

At least 397 records · Page 22Linked to original sources
PubMed1973

Myosin ATP hydrolysis: a mechanism involving a magnesium chelate complex.

It is suggested that under physiological conditions (> 1 mM Mg(2+)) MgATP binds to myosin to form a chelate involving the two reactive sulfhydryl sites (SH(1) and SH(2)). The stability of the chelate structure results in marked inhibition of the myosin ATPase in the presence of millimolar magnesium ion. The inhibitory effect of magnesium ion can be eliminated chemically by blocking either the SH(1) or SH(2) site since this precludes formation of the chelate. In muscle, actin apparently behaves in a similar fashion in that its interaction with myosin causes a disruption of the chelate structure.

Adenosine Triphosphatases↗
PubMed1972

Side effects of extinction procedures in a remedial preschool.

Several studies have shown that behavior modification procedures aimed at a single behavior may have effects on other, nonmanipulated behaviors. A young retarded boy engaged in excessive conversation with his preschool teacher. The teacher then began to ignore his initiated conversation during free-play periods, and it decreased. In addition, (1) social behavior relative to children increased, and (2) use of girls' toys decreased during free play. Also, (3) appropriate behavior at group academics declined, while (4) disruptions rose. In a second study, the teacher alternated conditions of praise and ignoring for talking with children. Talking with children varied accordingly. In addition, use of girls' toys and group academics disruptions rose during the ignoring condition. Appropriate behaviors dropped. Lastly, a timeout procedure was used to eliminate the undesirable side effects of disruptions and of use of girls' toys. Apparently, a response class may have member behaviors that covary directly and/or inversely. Some covariations may be socially desirable, others undesirable. The appearance of undesirable "side effects" can be controlled using behavior modification techniques.

Journal Article↗
PubMed1969

A comparison of the effects of ultraviolet and ionizing radiations on trypsin activity and on its constituent amino acids.

Photons of 254nm. u.v. light, (60)Co gamma-rays and 1Mev electrons produce different patterns of destruction of individual amino acids in dried films of trypsin and in the corresponding amino acid mixture. For example, in the amino acid mixture u.v. light destroys tyrosine, tryptophan and cystine, whereas in trypsin only cystine is disrupted but with 10 times the initial yield. Further, in the amino acid mixture loss of half-cystine is a simple exponential function of dose, but in trypsin there appear to be two exponential components of the loss with yields that differ by a factor of 35. Both the gamma-rays and electrons destroy half-cystine, tryptophan, histidine and methionine in the amino acid mixture with remarkably high yields, whereas in trypsin doses that destroy almost all of the enzymic activity produce no detectable destruction of amino acid residues. These marked differences between the two preparations show that the radiation-sensitivity of a given amino acid alone and in a protein is different, and suggests that in trypsin there is fairly extensive migration of energy, charge or both with localization of damage at specific sites determined by this enzyme's internal organization. All three types of radiation produce appreciable amounts of ;damaged' (not completely inactivated) molecules which are prevented from reassuming an active configuration by the addition of 5.5m-urea; thiol reagents have a similar effect after bombardment with u.v. light or electrons. The patterns of destruction produced by gamma-rays and by electrons in both the amino acid mixture and in trypsin are different (some of the yields vary by a factor of 30). This result appears to be inconsistent with the popular belief that most of the energy absorbed from gamma-rays is associated with very-high-energy electrons.

Amino Acids↗