Effects of extremely low frequency electromagnetic fields on the adenylate kinase activity of rod outer segment of bovine retina.

Extremely low frequency electromagnetic fields (ELF-EMFs) of 75 Hz with amplitudes above a threshold of about 125 microT have a dramatic effect on the adenylate kinase (AK) activity of the rod outer segment (ROS) membranes. In fact, the ATP production by ROS membranes or by purified disk membranes placed in the field decreased by approximately 54%. The decrease in enzymatic activity was independent of the time of exposure to the field and was completely reversible. When disk membranes were solubilized with Triton or a soluble isoform of AK was used, negligible effects of the field were obtained on the enzymatic activity, suggesting that the membrane has an important role in determining the conditions for the enzyme inactivation.

Electromagnetic field of extremely low frequency decreased adenylate kinase activity in retinal rod outer segment membranes.

Adenylate kinase activity in rod outer segment membranes of bovine retina decreased of about 55% when exposed to an extremely low frequency electromagnetic field of 75 Hz and 250 microT. The effect was independent of the time of permanence in the field. Negligible effects of the field were found on the enzymatic activity of a soluble isoform of adenylate kinase or of rod outer segment membranes solubilized with Triton, suggesting the importance of the membrane in determining the conditions of the enzyme inactivation.

Vanadate catalyzes photocleavage of adenylate kinase at proline-17 in the phosphate-binding loop.

Irradiation of adenylate kinase (AK) from chicken muscle with 300-400-nm light in the presence of 0.25 mM vanadate ion first inactivated the enzyme and then cleaved the polypeptide chain near the NH2 terminus. The addition of the multisubstrate analogue, P1,P5-bis(5'-adenosyl) pentaphosphate, prevented both effects. ATP, but not AMP, blocked both inactivation and cleavage in a saturable manner, suggesting that both effects were due to modification at the ATP-binding site. The polypeptide products of the photocleavage were isolated by HPLC and characterized by amino acid composition, peptide sequencing, and mass spectral analyses. The predominant (greater than 90%) small peptide fragment contained the first 16 amino acids from the amino terminus of the enzyme. The amino terminus of this peptide contained an acetylated serine, and the "carboxy" terminus was modified by a cyclized gamma-aminobutyric acid which originated from photooxidation and decarboxylation of proline-17 by vanadate. Edman sequencing indicated that the majority of the large peptide fragment (Mr approximately 19,500) was amino-terminal blocked, but a small portion was sequenceable starting at either glycine-18 (7%) or serine-19 (2%). These studies indicate that in the ATP-AK complex proline-17 is close to the phosphate chain of ATP but not AMP, consistent with the latest evaluation of nucleotide-binding sites on mitochondrial matrix AK by X-ray crystallography [Diederichs, K., & Schulz, G.E. (1991) J. Mol. Biol. 217, 541-549]. Furthermore, this is the first report that an amino acid other than serine can be involved in vanadate-promoted photocleavage reactions.

Helium-neon laser irradiation of rat liver mitochondria gives rise to a new subpopulation of mitochondria: isolation and first biochemical characterization.

An experiment was performed to isolate the small atypical mitochondria produced during the irradiation of normal mitochondria with an He-Ne laser. Rat liver mitochondria were irradiated with a low-power continuous-wave He-Ne laser (energy dose, 5 J cm-2), followed by isolation using a sucrose gradient. In the irradiated sample, two bands were observed, one corresponding to normal mitochondria and the other to atypical mitochondria. Certain biochemical features of the mitochondria were investigated: mitochondrial enzyme activity and the presence of DNA and RNA were demonstrated. Hybridization experiments carried out with labelled mitochondrial probes, containing the genes for cytochrome oxidase subunit I and 12S rRNA, confirmed the mitochondrial nature of the isolated RNA.

Photosensitization of mitochondrial adenosine-triphosphatase and adenylate kinase by hematoporphyrin derivative in vitro.

Mitochondrial ATPase and adenylate kinase activity of hepatoma cells were inhibited by hematoporphyrin derivative (HPD) followed by photoirradiation. Inhibition of ATPase activity was a dose- and time-related event. Malonaldehyde (MDA) content of mitochondrial membranes was markedly increased by HPD plus light. The content of mouse liver microsomal cytochrome P-450 was greatly increased after intraperitoneal injection of HPD for 4 days (5 mg/kg/day). The liver weight, and levels of liver microsomal G-6-phosphatase, MDA and triglyceride (TG) showed no difference in treated vs. control animals. The data presented here demonstrate that mitochondria may be a sensitive site of action of HPD photosensitization, and inactivation of ATPase and adenylate kinase may be an important contributing factor to tumor cell damage and death.

[Adenylate kinase activity of the blood of irradiated rats]. / Aktivnost' adenilatkinazy v krovi obluchennykh krys.

The direct and reverse adenylate kinase reactions were studied in blood of rats 1, 3, 7, 15 and 30 days after total X-ray irradiation with a dose of 154.8 mC/kg (600 R) dose. It is found out that adenylate kinase (CE 2.7.4.3) activity in leucocytes and erythrocytes is inhibited on the 3d, 7th and 15th days of the study. Inhibition of the reverse adenylate kinase reaction is pronounced to a greater extent than that of the direct one. The adenylate kinase of erythrocytes is more stable to the effect of ionizing radiations as compared to this enzyme of leucocytes. When the enzymic activity in the blood cells is inhibited, the activity of the direct adenylate kinase reaction in the serum increases significantly and that of the reverse one remains unchanged.

Influence of light on activity of adenylate kinase and pterin-protein complexes from pea chloroplasts.

The activity of adenylate kinase (AK) and of pterin-protein complexes (PPC), whose proteins have adenylate kinase activity comparable to that of the enzyme was studied. It was established that light inhibits adenylate kinase activity and that this effect is partially eliminated by phosphate ions. The forward and reverse reactions catalyzed by AK and PPC were studied and it was found that the activity of native protein complexes is different in the forward and reverse reactions. The thermostable protein both of adenylate kinase and of the pterin-protein complexes had identical activity in the ADP dismutation and the reverse reaction.

Measure of enzymatic activity coincident with 2450 MHz microwave exposure.

Enzyme preparations were exposed to microwave radiation at 2450 MHz and enzymatic activity was simultaneously monitored spectrophotometrically with a crossed-beam exposure detection system. Enzymes studied were glucose 6-phosphate dehydrogenase from human red blood cells and yeast, adenylate kinase from rat liver mitochondria and rabbit muscle, and rat liver microsomal NADPH cytochrome c reductase. No difference was found between the specific activity at 25 degrees C of unirradiated controls and enzyme preparations irradiated at an absorbed dose rate of 42 W/kg.