Elena Puszkin

Actomyosin-like protein isolated from mammalian brain.

A protein with characteristics similar to actomyosin has been isolated from whole brain of rat and cat. It is soluble in 0.6 molar potassium chloride and insoluble in 0.1 molar potassium chloride. It superprecipitates with magnesium ions and adenosine triphosphate. It has adenosine triphosphatase activity stimulated by either magnesium or calcium ions. Both superprecipitation and adenosine triphosphatase activity are inhibited by p-chloromercuribenzoate and Mersalyl but not by ouabain.

Functional Changes in Platelets During Extracorporeal Circulation

An in vitro trauma test was conducted to determine the effects of extracorporeal circulation on platelet count and function. Fresh human blood was circulated in two identical in vitro circuits for six hours at a rate of 500 ml per minute (500 recirculations). One circuit included a G.E.--Peirce membrane lung and the other was a control. Platelet aggregation induced by adenosine diphosphate (ADP), epinephrine, or collagen was studied before and after six hours of perfusion. No important drop in platelet count occurred in the control circuit (Control-C) following bypass, but there was a 20% drop for the lung circuit (Lung-C). Platelet aggregation was reduced by about 30% for the control circuit and 65% for the lung circuit. The large decrease in platelet function accompanied by only a moderate decrease in platelet count is discussed in terms of loss of the youngest and most active platelets, platelet inhibition due to ADP released by red blood cell lysis, and platelet trauma.

Control of platelet actomyosin activity: Effect of ADP on superprecipitation and ATPase activity of human platelet actomyosin ☆

Abstract 1. 1. Platelet actomyosin superprecipitation performed in 0.09 M to 0.12 M KCl showed a biphasic curve with clearing and turbidity increase after addition of Mg-ATP. 2. 2. Addition of ADP produced inhibition of the duration and extent of the clearing phase (Km of 4 · 10−5 M), and activation of the superprecipitation phase (Km of 1.96 · 10−5 M). 3. 3. The effect of ADP was observed with no significant increase of ATPase activity and was apparently specific for ADP and not for GDP, UDP, or IDP when superprecipitation was initiated only with Mg-ATP. 4. 4. The effect of ADP was observed when superprecipitation occurred in the presence of EGTA. These data suggest that ADP may form part of a control mechanism of platelet contractile activity.

Human platelets: amino acid synthesis.

Summary The rapid incorporation of labeled 14C from U-14C-acetate and U-14C‐ D‐glucose into free glutamic acid, glutamine, aspartic acid, and asparagine shows that human platelets are capable of synthesizing their own amino acids. Differences in the turnover rates of these amino acids indicate that the metabolic pools are localized in compartments. It is also suggested that more than one pool of acetyl CoA and probably at least two separate pools of citric acid cycle intermediates exist.