A simple and rapid method for the determination of thiocyanate in serum.

Studies were performed to evaluate ultrafiltration as a means for isolating thiocyanate from serum prior to its colorimetric determination as a ferric chloride complex. Recovery of thiocyanate from serum was enhanced by addition of alkali prior to preparation of the ultrafiltrate, and averaged 96.8%. The reproducibility (CV) of test was 2.3%, within-day; and 3.3%, between-day. The colorimetric reaction was linear to 100 micrograms/mL. The method was tested by determining thiocyanate concentrations in samples collected from smoking and nonsmoking individuals. Thiocyanate concentrations in patient samples, collected after IV-infusion of nitroprusside, were scattered around those of the general population, and ranged from 0.3 to 20 micrograms/mL.

Assays of serum lipase: analytical and clinical considerations.

We evaluated three commercially available methods for determining lipase (EC 3.1.1.3) in serum--the Du Pont aca, Boehringer Mannheim Diagnostics (BMD), and Kodak Ektachem (EK) procedures--for their analytical properties and diagnostic efficiencies. Titrimetry was used as the comparative method. The BMD and EK methods showed better agreement with the titrimetric method, owing to the presence of the necessary cofactor, colipase, in their reagents. Colipase also increased the analytical sensitivity of the BMD and EK procedures as compared with the aca method. Determinations of serum lipase, by all methods, had a clinical sensitivity in excess of 80% for acute pancreatitis; the specificity of the lipase test was about 60%, or twice that of serum amylase. Serum lipase determinations with the current, simpler technology are superior to total amylase in the diagnosis of patients with acute pancreatitis. When a colipase-supplemented method is used, a serum lipase value greater than 10-fold the upper reference limit appears to be pathognomonic for acute pancreatitis or inflammation of organs close to the pancreas.

Inhibition of coenzyme activation of aspartate aminotransferase.

Forty compounds were surveyed for their effect on the activation of pig heart apoaspartate aminotransferase by pyridoxamine 5'-phosphate. Most of the nucleotides, sugar phosphates, coenzymes, phospholipid precursors and inorganic oxyanions tested were found to be inhibitory. With few exceptions, the only requirement for a substance to be inhibitory is the presence of a di- or polyanionic moiety analogous to the 5'-phosphate group of the cofactor. In spite of the lack of overall structural similarity to pyridoxamine 5'-phosphate, inorganic pyrophospate and apparently other inhibitors are characterized by dissociation constants comparable in magnitude to that previously reported for the natural cofactor. The physiological significance of the inhibition of coenzyme activation of apoaspartate aminotransferase by these common biological compounds is not known.