Reasons for disorders of fatty acid oxidation in isolated heart mitochondria during ischemia

The influence of malate and cytochrome c on fatty acid oxidation under control and ischemic conditions was investigated. In the medium without malate, cytochrome did not make fatty acid oxidation decreased during ischemia return to normal. Oxidation in the media containing malate and cytochrome did not differ from control only when it was measured after preliminary oxidation of endogenous substrates. The ratio of palmitoyl-CoA and palmitoyl carnitine to the respiration rates at state 3 was unchanged at 60 min ischemia. Apparently, no changes in carnitine acyltransferase playing a role in oxidation of palmitoyl-CoA took place. Thus, the decrease of fatty acid oxidation at early periods of ischemia is largely caused by a reduction in the content of cytochrome c and intermediates of Krebs cycle in the mitochondria.     

Mechanistic studies on carboxypeptidase a from goat pancreas — part II: Evidence for carboxyl group

Studies with substrate analogues and the pH optimum indicated the involvement of carboxyl group in the active site of goat carboxypeptidase A. Chemical modification of the enzyme with 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide methoI -p-toluene sulphonate, a carboxyl specific reagent, led to loss of both esterase and peptidase activities. Protection studies showed that this carboxyl group was in the active site and was protected by Βp-phenylpropionic acid and glycyl-L-tyrosine. Kinetic studies also confirmed the involvement of carboxylic group because the enzyme modification with water soluble carbodiimide was a two step reaction which excluded the possibility of tyrosine or lysine which are known to give a one step reaction with this reagent     

Effect of etmozin on thrombocyte aggregation capacity

It was shown in in vitro experiments that etmozin at a concentration of 100 micrograms/ml significantly suppressed (by 21%) platelet aggregation induced by ADP, but it had no effect on platelet aggregation induced by arachidonic acid. In in vivo experiments etmozin was found to cause a marked suppression of tendon collagen-induced platelet aggregation in the doses 2-5 mg/kg having antiarrhythmic activity. Under suppressed platelet aggregation induced by indomethacin, the prostaglandin biosynthesis blocker etmozin displayed no antiaggregation effect. It is suggested that etmozin effects on ADP release from platelets play the main role in the mechanism of its antiaggregation action.     

Two types of eye movements during electrical stimulation of the rostral and caudal parts of the medial frontal "oculomotor" area in cats

The character of eye movements during electrical stimulation of the medial wall of the brain beneath the cruciate sulcus and of the inferior wall of the cruciate sulcus itself in the frontal cortex was investigated in waking cats. Stimulation of this part of the brain evoked two types of eye movements: unidirectional concomitant saccades, whose direction and amplitude were independent of the original position of the eyes in the orbits, and saccades into the central position (so-called centering saccades). Unidirectional saccades appeared in response to stimulation of the caudal part of the investigated zone, centering saccades in response to stimulation of its rostral part. Analysis of the directions and amplitudes of unidirectional saccades suggested the retinotopic organization of the caudal zone. Systematic changes in the magnitude and direction of vertical saccades during stimulation of the deep parts of the cruciate sulcus indicated previsely the projection of the vertical meridian of the retina. Reappearance of vertical saccades evoked by stimulation of certain parts of the medial wall of the brain suggests the existence of more than one retinotopically organized zone in this region. Inconstancy of stereotaxic coordinates of the oculomotor area, studied in different animals, was noted.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 761–766, November–December, 1984.     

Microcalorimetric assay of acetylcholinesterase

Comparative assays were made in a spectrophotometer and a microcalorimeter for the reaction between acetylcholinesterase (EC 3.1.1.7) and acetylthiocholine. The rate of light absorbance change and the rate of heat flow were measured from similar and simultaneous reactions in spectrophotometer and microcalorimeter, respectively. At the enzyme activity levels studied, i.e., 0.05–0.15 I.U. in calorimetry and 1–4 I.U. in spectrophotometry, the reaction rates were linear and showed first-order kinetics. A highly significant positive correlation was seen between the two methods (r = 0.997). More importantly, spectrophotometric assay with acetylthiocholine (which utilized a secondary reaction with chromagen, dithiobisnitrobenzoic acid) stood in highly significant positive correlation with calorimetric assays (which did not require a chromagen) either with the same substrate (r = 0.976) or with acetylcholine (r = 0.900). It appears that microcalorimetry can be used in preference to spectrophotometry for enzyme kinetic studies to overcome the complexity of reaction mixture and interference problems and with the advantage of using natural substrates.