We describe a continuous-flow, automated determination of total cholesterol in serum, which is based on enzymatic hydrolysis of cholesterol esters, oxidation of cholesterol by cholesterol oxidase, and colorimetric measurement of liberated perioxide with 4-aminoantipyrine, phenol, and peroxidase. Free cholesterol is determined with the same AutoAnalyzer II manifold and reagents, except that cholesterol esterase is omitted from the reagent. Cholesterol-in-serum materials that have been assayed by an established method are used for calibration. We found this approach to be necessary because primary cholesterol standards in organic solvents are incompatible with the aqueous reagent. Results of the enzymatic total cholesterol method correlated well with those by an AutoAnalyzer II method which involves an extraction with isopropanol and the Liebermann-Burchard color reaction (total cholesterol, g/liter, yenz= 0991xlb +0.05;r=0.996). Results of the enzymatic free cholesterol procedure agreed satisfactorily with one in which free cholesterol is precipitated as the digitonide and subsequently analyzed colorimetrically with the Liebermann-Burchard reaction (free cholesterol, %, yenz = 0.982xdig -0.7;r= 0.956).

We describe an enzymatic method, requiring only 10 mul of serum, for determining CO2 as bicarbonate or dissolved gas. Phosphoenolpyruvate carboxylase catalyzes the reaction of HCO3- with phosphoenolypyruvate to give oxalacetate. The resulting NADH, in the presence of malate dehydrogenase, is oxidized to NAD+, and the decrease in absorbance at 340 nm is directly proportional to the amount of CO2 present in the sample. Reaction is complete in 3 to 6 min under assay conditions, and is linearly related to CO2 concentrations between 8 and 65 mmol/liter. Analytical recovery is 95-110% (average, 101%). Two laboratories compared values obtained by continuous-flow analysis. The resulting correlation coefficients were 0.966 and 0.987, values for the t-test were t(paired) equals 0.473 and t(paired) equals 0.334, and average day-to-day precisions (three concentrations) were 3.9% and 4.2%.

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A study was made of the in vitro phosphorylation of some nucleosides in cell-free extracts from a thioguanine-resistant subline of Ehrlich ascites carcinoma which lacked inosine monophosphate – guanosine monophosphate pyrophosphorylase. The results indicated that there were kinases which catalyzed the phosphorylation of a variety of nucleosides. Ribofuranosyl-6-thiopurme was phosphorylated whereas the xylofuranosyl-, arabinofuranosyl-, and lyxofuranosyl-6-thiopurine were not substrates. The xylose and ribose derivatives of 6-methylthiopurine were phosphorylated but the arabinose derivative was not. Guanosine and some of its analogs were also phosphorylated but no correlation could be found between structure and phosphorylation of the guanosine analogs tested.The reaction showed dependence on the addition of divalent cation and an ATP-regenerating system.