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Biomedical subjects

F L Call

Publications and source records attributed to F L Call.

8 recordsLinked to original sources
PubMed1975

Synthesis of ethanolamine phosphoglycerides by human platelets.

Platelet homogenates contain an ethanolaminephosphotransferase (EC 2.7.8.1) that catalyzes the synthesis of ethanolamine phosphoglycerides from cytidine-5'-diphosphate ethanolamine and 1-radyl-2-acyl-sn-glycerols. The enzyme is particulate-bound and requires Mn2+ and bile salts for optimal activity. The apparent Km of the enzyme for cytidine-5'-diphosphate ethanolamine is 1.6 X 10(-5) M when the concentration of 1,2-diacyl-sn-glycerols is 8.8 X 10(-4) M. The pH optimum is 8.5 in Tris-HCl or glycine-NaOH buffer. The activity of the enzyme in platelets from normal subjects is 0.24-0.34 nmole/min/mg of protein.

Blood Platelets↗
PubMed1973

Diglyceride kinase in human platelets.

Human platelets contain diglyceride kinase, an enzyme that catalyzes the phosphorylation of diacylglycerol by adenosine 5'-triphosphate to yield phosphatidic acid. The majority of the platelet enzyme is particulate-bound, and membrane fractions of platelet homogenates have a higher specific activity than granule fractions. Both deoxycholate and magnesium are necessary for optimal enzyme activity. The K(m) of the enzyme for adenosine 5'-triphosphate is 1.3 mm, and the apparent K(m) for diacylglycerol is 0.4 mm. The pH optimum is 6.6-6.8 in imidazole-HCl or maleate-NaOH buffer. The enzyme activity of platelets from normal subjects was similar to the activity from patients with renal and hepatic failure.

Adenosine Triphosphate↗
PubMed1970

Biosynthesis of cytidine diphosphate diglyceride by human platelets.

Homogenates of human platelets contain an enzyme which catalyzes the formation of cytidine diphosphate diglyceride from cytidine triphosphate and phosphatidic acid. The enzymatic activity could not be dissociated from platelet particles and the greatest specific activity was found in the membrane fraction. The K(m) for cytidine triphosphate was 0.16 mmole/liter and the apparent K(m) for phosphatidic acid was 6.2 mmoles/liter. The pH optimum was 7.0 and the most effective buffers were triethanolamine-HCl and Tris-HCl. The reaction was dependent on the presence of divalent cations, magnesium being the most effective of those investigated. Monovalent cations did not alter the reaction rate. Evidence is presented that the cytidine diphosphate diglyceride produced can serve as a precursor for the synthesis of phosphatidylinositol. No difference was found in the enzymatic activity in platelets from normal subjects and from patients with diseases known to interfere with platelet thromboplastic function.

Blood Platelet Disorders↗
PubMed1970

The biosynthesis of phosphatidylinositol in human platelets.

Homogenates of human platelets can mediate the synthesis of phosphatidylinositol from myoinositol and cytidine diphosphate diglyceride. The cytidine diphosphate diglyceride: myoinositol, phosphatidyl transferase activity is particulate-bound, and the highest specific activity is found in the membrane fraction. The production of phosphatidylinositol is decreased by sulfhydryl-binding agents, and the addition of thiols to the platelet homogenates increases the enzymatic activity. The reaction exhibits a pH optimum of 8.5-9.0. Divalent cations stimulate the reaction, and manganous chloride was the most effective of those investigated. The K(m) of the enzyme for myoinositol is 0.27 mM, and the K(m) for cytidine diphosphate diglyceride is 0.53 mM. The enzymatic activity of platelets isolated from patients with several diseases known to interfere with platelet clotpromoting function is similar to the enzymatic activity of platelets from normal donors.

Blood Platelets↗