Further observations on the differential precipitation of alkaline phosphatase isoenzymes by ethanol

The proportions of the total activities of different isoenzymes of human alkaline phosphatase precipitated from serum by ethanol (20% v/v) were: liver phosphatase, 37%; placental phosphatase, 23%; bone phosphatase, 8.0%, and small-intestinal phosphatase, 3.7%. Treatment of the isoenzymes with neuraminidase reduced the percentages of non-intestinal phosphatases precipitated by ethanol to below 10%. Precipitation of intestinal alkaline phosphatase was unaffected by this treatment. The degree of solubility in ethanol therefore appears to be largely determined by the content of terminal sialic acid residues in the alkaline phosphatase molecules. In contrast the stabilities of the isoenzymes to heating at 56 degrees C were not significantly altered by neuraminidase digestion.

Activities of bone and liver alkaline phosphatases in serum in health and disease

A heat-inactivation method for determining absolute activities of liver and bone alkaline phosphatases in serum has been applied extensively in routine diagnosis. Values for each isoenzyme in healthy individuals of different ages are reported together with results obtained in various diseases. Data from normal subjects show that bone alkaline phosphatase contributes about half the total alkaline phosphatase activity in adults. Liver phosphatase shows a slight increase with age. The method is also able to detect reliably the presence of carcinoplacental isoenzymes.

An automated continuous-monitoring procedure for the determination of acid phosphatase activity in serum

The method of Hillmann, in which hydrolysis of alpha-naphthyl phosphate by acid phosphatase is coupled to the formation of an alpha-naphthol-Fast Red TR azo-compound, has been adapted for use with the LKB Produkter AB 8600 reaction rate analyzer. Factors which affect the reproducibility of the method are described and its performance is shown to be superior to that of a manual phenyl-phosphate procedure.

Enzyme activities of cells of different types isolated from livers of normal and cholestatic rats

1. The distribution of three membrane-bound enzymes, alkaline phosphatase, 5′-nucleotidase and γ-glutamyl transferase, has been examined in rat liver fractionated into parenchymal cells, a Kupffer cell fraction and a biliary tract fraction by perfusion with collagenase solution.

2. In control rat livers the highest enzyme concentrations were found in Kupffer cell preparations. The fraction enriched with biliary tract cells showed concentrations two- to fourfold those in isolated parenchymal cells.

3. At 24 h after ligation of the bile duct there was a fourfold increase in the alkaline phosphatase activity in parenchymal cells and a 2·5-fold increase of the same enzyme in the biliary tract fraction. The concentration of alkaline phosphatase in Kupffer cells remained unchanged.

4. 5′-Nucleotidase and γ-glutamyl transferase concentrations tended to decrease after bile-duct ligation for 24 h, the most marked changes being found in Kupffer cells.

5. After bile-duct ligation for 7 days the overall activities of hepatic alkaline phosphatase and γ-glutamyl transferase increased fourfold and there was a small rise in 5′-nucleotidase. For alkaline phosphatase and γ-glutamyl transferase the changes were found primarily in parenchymal cells and in the biliary tract fraction. There was a small rise in the activity of 5′-nucleotidase in parenchymal cells and a fall in activity in Kupffer cells.

6. These data show marked differences in the distribution and behaviour of three enzymes which are often used as alternatives in the assessment of patients with liver disease.

The scientific foundations of clinical enzymology

Clinical enzymology is the study of the activity and properties of enzymes in specimens (usually of blood) taken from patients, as an aid to the diagnosis and understanding of disease. Research in many areas of enzymology is undertaken to strengthen the foundations on which the clinical interpretation of such enzyme measurements rests. Some aspects of this research are briefly described.

Apoenzyme of aspartate aminotransferase in serum in health and disease

Aspartate aminotransferase activity has been measured in the sera of normal subjects and in patients with various diseases both with and without addition of pyridoxal phosphate to the assay medium. Considerable quantities of apoaminotransferase were present in almost all samples. In normal subjects this potentially-active enzyme corresponds on average to about half the holoenzyme present before reactivation with pyridoxal phosphate. However, considerable variations between individuals were found in the amounts of apoaminotransferase present in serum, and also between groups of patients with various diseases.

Titration of human placental alkaline phosphatase with radioactive orthophosphate

Human placental alkaline phosphatase incorporates radioactive phosphate specifically and covalently at acid pH. By titration of solutions of the purified enzyme with radioactive orthophosphate, the enzyme was shown to incorporate up to 2 phosphate groups per molecule. No evidence was found to suggest that the two sites had different affinities for phosphate. Similar titrations can be used to determine the molarity of solutions of non-placental alkaline phosphatases of unknown purity, if these also are assumed to possess 2 binding sites per molecule.

An active site peptide from human placental alkaline phosphatase

A preparation of human placental alkaline phosphatase was labelled covalently at the active site with [32P]orthophosphate. Treatment with trypsin gave essentially one radioactive peptide, the active site peptide, of approximately 2300 molecular weight. Dansylation of the peptide showed that the amino-terminal residue was glycine. After acid hydrolysis the only radioactively-labelled amino acid present was serine phosphate. The amino acid composition was similar to those compositions reported for active site peptides from other alkaline phosphatases.

Reactivation of the apoenzyme of aspartate aminotransferase in serum

Apoenzyme of aspartate aminotransferase in serum can be reactivated conveniently by addition of 100 mumoles/l pyridoxal phosphate to the reaction mixture, without extending the usual minimum pre-incubation period in the operation of the LKB 8600 reaction rate analyzer. Normal sera contain some apoenzyme, the amount of which, as well as that of holoenzyme, is greatly increased by damage to skeletal muscle. This may be due to direct injury or to the indirect effects of anoxia; e.g., following surgery with extracorporeal circulation. Myocardial infarction also increases the levels of both apo- and holoenzymes, but changes in the two levels follow similar time courses and apo- and holo-aminotransferases disappear from the circulation at similar rates.

Some properties of alkaline-phosphatases in parenchymal and biliary tract cells separated from rat liver

Livers of both normal and bile-duct ligated rats have been separated into parenchymal cells and fractions enriched in biliary tract cells. The specific activity of alkaline phosphatase increases in both types of cells after occlusion of the bile duct but the increase is more marked in the case of parenchymal cells. The enzyme from parenchymal cells migrates as a single zone on electrophoresis, whereas additional zones of lower anodal mobility occur in extracts of biliary tract preparations. The alkaline phosphatase activity of the slower zones is significantly less stable to heat than that of the zone characteristic of parenchymal cells. It is postulated that the increase in heat stability of alkaline phosphate in extracts of whole rat liver after bile-duct ligation is due to an increase in the proportion of the more stable form of the enzyme predominant in parenchymal cells.

A simplified heat-inactivation method for investigating alkaline phosphatase isoenzymes in serum

A method is described for the determination of the percentage of liver alkaline phosphatase in serum samples in which measurements of residual activity are made after incubating the samples for 15 and 25 min at 56 degrees C. This method has the advantage of taking into account quantitative variations in the heat stability characteristics of liver alkaline phosphatase from one sample to another, in contrast to methods in which only a single period of exposure to 56 degrees C is employed.

Incidence and some properties of an electrophoretically slow form of alkaline phosphatase in sera of patients with diseases of the intestine

A zone of alkaline phosphatase activity migrating at about 40 percent of the rate of liver phosphatase in gel electrophoresis has been detected in sera from 2 out of 22 cases of ulcerative colitis and 1 out of 32 cases of Crohn's disease, but in no other specimen from 33 patients with other diseases of the digestive tract. This rare form of alkaline phosphatase was unlike small-intestinal alkaline phosphatase in several properties. Its appearance in association with diseases of the colon suggests that the rare isoenzyme may originate in that organ. However, the slowly migrating alkaline phosphatase was equally prominent in serum specimens taken before and after operation in one patient who underwent a pan-proctocolectomy for the alleviation of uncontrollable ulcerative colitis.

Analysis of heat inactivation curves of alkaline phosphatase isoenzymes in serum

The course of the decline in alkaline phosphatase activity during exposureof serum samples to a temperature of 56 degree C can be resolved into two phases. These represent the exponential decay of an enzyme component with an average half-inactivation time of 112 seconds and of a second component with an average half-inactivation time of 456 seconds. The more rapid fall is due to inactivation of bone alkaline phosphatase and the slower to inactivation of liver and, when present, intestinal phosphatases. The half-inactivation times of the different enzyme species show considerable variation from one serum sample to another. The implications of this variation for methods of estimating the relative proportions of alkaline phosphatase isoenzymes by selective inactivation procedures are discussed.