R. H. S. Thompson

PHOSPHOLIPASE-A ACTIVITY OF MAMMALIAN TISSUES.

Abstract 1. 1.The phospholipase-A (phosphatide acyl-hydrolase, EC 3.1.1.4) activity of extracts of a number of different rat tissues has been determined by estimating the decline in the concentration of lecithin together with the increase in the concentration both of fatty acids and of lysolecithin, that occurs when the extract is incubated with lecithin under suitable conditions. 2. 2.Wide variations in the level of activity in different tissues were noted; apart from the high levels in pancreas and small intestine, moderately high activity was found in testis, spleen, lung liver. 3. 3.Using rat testis, it has been shown that the greatest activity is present in glycerol-treated extracts of acetone-dried powders of the tissue.

Fatty acid composition of phospholipids from platelets and erythrocytes in multiple sclerosis

The fatty acid composition of the phospholipids of red blood cells and blood platelets has been investigated in multiple sclerosis patients and in normal individuals. The variation in the platelet phospholipid fatty acid pattern in normals has been measured for the first time and has been shown to be small. The relative level of linoleate, expressed as a percentage of the five main fatty acids, was found to be significantly lower in the multiple sclerosis patients than in healthy individuals, both in the red cells and platelets. A highly significant correlation was found between serum linoleate and both platelet and red cell linoleate.

Linoleate metabolism in multiple sclerosis

(1) The levels of oleate and linoleate in the serum have been measured in 14 patients with multiple sclerosis (MS) and in 14 healthy subjects before, during and after a five day period when the normal diet was supplemented with linoleate. (2) In confirmation of earlier work the mean percentage of linoleate in the serum lipids of the MS patients was significantly lower (P < 0·01) than in the control subjects in the pre-supplementation period. The mean percentage of oleate showed an increase (P < 0·005) in the patients as compared with the controls while on their normal diets. (3) The period of linoleate feeding produced a considerable rise in the percentage of linoleate together with a fall in the percentage of oleate in both the controls and the MS patients. (4) When large amounts of linoleate, as present in sunflower seed oil, are ingested we have been unable to obtain evidence of a defect in absorption from the intestinal lumen.

Relationship between plasma and lymphocyte linoleate in multiple sclerosis.

The linoleate level in total lipids was measured in lymphocytes from control subjects and patients with multiple sclerosis. A small but significant decrease was found in cases of multiple sclerosis. The percentage composition of lymphocyte fatty acids was determined in rats fed diets with various linoleate contents. There was a correlation between lymphocyte linoleate and plasma linoleate in both humans and rats.

THE LIBERATION OF ACTIVE ENZYMES FROM BRAIN TISSUE BY LYSOLECITHIN

IN 1951, ORD and THOMPSON described the ability of a number of surface-active agents to ‘clear’ the opaque supernatants obtained by the centrifugation of water homogenates of whole rat brain. In an attempt to purify the true cholinesterase of brain they further showed that a non-ionic surface-active agent, acetyl alcoholpolyoxyethylene condensate, was able to ‘solubilize’ this enzyme without causing any inactivation. GROSSE and TAUBOCK (1942) had earlier briefly reported that a brain brei suspended in physiological saline can be cleared with lysolecithin. A more detailed description of this action of lysolecithin on nervous tissue has recently been given by WEBSTER (1957), who has shown that when uncentrifuged homogenates of whole brain tissue are incubated at 38”c with lysolecithin, a very rapid and almost complete ‘clearing’ of the opaque homogenate occurs; following a 2 hr incubation with 0.007 M-lysokcithin, the optical transmission, using a neutral grey filter, of a 1 : 20 homogenate of rat brain in 0.025 M-sodium bicarbonate is equal to about 80 per cent of the optical transmission of water, while about 60 per cent optical transmission is reached after only 10 min incubation; the optical transmission of the homogenate at zero time was 5 per cent of that of water. In view of this ‘solubilizing’ effect on the greater part of the components of the neurones, glial cells and myelin sheath lipids present in these homogenates, it seemed of interest to determine next what effects, if any, the lysolecithin, and the lysis produced by this compound, might have on the enzymic activities of the original homogenates. WEIL (1930) had earlier studied the effect of cobra venom, now known to contain a phospholipase A , on segments of spinal cord, and MORRISON and ZAMECNIK (1950), on the basis of similar observations, had suggested that if lysolecithin were to be formed inside the nervous system, localized demyelination might be expected to occur. We have therefore, in the first instance, been primarily interested in those enzymes which, if released into solution, might be expected to exert a further destructive action on cclls or cell membranes, or which might interfere with the normal processes of excitation and transmission in unaffected nervous tissue. We have begun by assaying in lysolecithin-cleared preparations the levels of activity of the cholinesterases and of mono-amine oxidase, enzymes which are or may be concerned with the inactivation of transmitter or excitor substances, and of the proteinases, esterases, phosphatases and transaminases, which might be expected, if working in an unco-ordinated fashion, to exert degradative changes on the normal cells. A preliminary account of part of this work has already been published (MARPLES, THOMPSON and WEBSTER, 1957). From the point of view of any possible pathological significance, it would clearly be desirable to know what effect, if any, lysolecithin

Further studies on platelet adhesiveness and serum cholesteryl linoleate levels in multiple sclerosis.

Earlier work indicated a fall in the level of linoleate, determined by gas chromatography, in the serum of patients in the active phases of multiple sclerosis (Baker, Thompson, and Zilkha, 1964; 1966). In a series of 35 patients with multiple sclerosis the level in the serum of the cholesteryl linoleate fraction, separated by thin-layer chromatography, was reduced in patients with clinical evidence of recent deterioration (Baker, Sanders, Thompson, and Zilkha, 1965).

Plasma phospholipids and their fatty acid composition in multiple sclerosis

Patients with multiple sclerosis, in whom there is evidence of recent clinical deterioration, have been shown to exhibit a reduction both in the proportion and in the absolute level of linoleic acid in the serum (Baker, Thompson, and Zilkha, 1964, 1966). Since the cholesteryl ester fraction of the plasma lipids contains a much higher proportion of linoleic acid than either the phospholipid or triglyceride fractions, the levels of cholesteryl linoleate in serum from normal subjects and from patients with multiple sclerosis have also been investigated (Baker, Sanders, Thompson, and Zilkha, 1965). It was found that the amount of this fraction of the total serum linoleate is strikingly reduced in patients in the active stages of this disease; the reduction in the level of cholesteryl linoleate in the most seriously affected group of patients amounted to 73% of the reduction in total linoleate. Since it is known that transesterification processes between the cholesterol and the ,-linked unsaturated fatty acid of certain of the phospholipids can take place in the serum (Glomset, Parker, Tjaden, and Williams, 1962; Glomset, 1962, 1963), it was decided, in view of these marked changes in the level of cholesteryl linoleate, to investigate also the plasma phospholipids and their fatty acid composition.

Hydrolysis of phosphoryl choline and related esters by the phosphomonoesterases of animal tissues

Abstract 1. 1. Although readily hydrolyzed by the alkaline phosphatase of brain, it has been shown that phosphorylcholine, phosphorylethanolamine, phosphorylserine, and phosphorylthreonine are only hydrolyzed very slightly (1.5–6% the rate of splitting of phenyl phosphate) by the acid phosphatase in the brains of man, dog, rabbit, hen, guinea pig, and the rat. 2. 2. A similar relative inactivity toward N-containing phosphate esters of this type has been shown for the acid phosphatases of human kidney, prostate, liver, and intestine. 3. 3. Experiments with inhibitors and activators have not so far yielded evidence of more than one alkaline phosphatase in brain, although they do not exclude this possibility.