Biochemistry of alkaline phosphatase isoenzymes

A neglected requirement for optimizing treatment of age-related osteoporosis: Replenishing the skeleton's base reservoir with net base-producing diets

Osteoporosis is a disorder of bone in which the mass of the bone is reduced and the bone's architecture at the microscopic level is disordered. Together those abnormalities predispose affected individuals to experience fractures despite only minimal trauma (i.e., fragility fractures). Age related osteoporosis is a common type of osteoporosis that occurs with aging in both men and women usually beginning after the age of peak bone mass. Research has found that the disorder can be partially reversed by reducing the net amount of acid that is produced when consuming typical Western diets. However, the amelioration that results has not been so dramatic or so consistent that physicians have adopted the procedure as part of the standard treatment for age-related osteoporosis. We propose that reducing the net acid load from the diet is not sufficient to reverse age related osteoporosis because it fails to supply base needed to restore the large amount of base in bone that had been lost by reacting with the net acid load of the diet that had been consumed for years or decades. Reducing the net acid load from the diet might be expected to have little ameliorative effect or merely slow the progression of the disorder. We hypothesize that both to restore osteoporotic bone to, or nearly to, its pre-disease state, as well as to eliminate the risk of fragility fractures, requires consuming diets that produce net amounts of base to restore the base lost from years to decades of consuming diets that produce net amounts of acid. We hypothesize also that the excess base and attendant subclinical metabolic alkalosis will both stimulate the cellular process of bone formation and suppress the cellular process of bone resorption, and thereby implement the restorative process.

Assessment of markers of bone formation under controlled environmental factors and their correlation with serum minerals in adult sheep as a model for orthopaedic research

Eighteen healthy skeletally mature (3 years old) ewes, with an average weight of 45 kg, of the Portuguese Churra da Terra Quente breed were used to evaluate the normal values of total and bone-specific isoform of alkaline phosphatase serum activities (ALP and BALP, respectively) and serum osteocalcin (OC) and their correlation with the serum minerals - calcium (Ca), phosphorus (P), magnesium (Mg) and ionized calcium (Ca(2+)). The sheep were maintained under controlled environmental conditions (constant diurnal photoperiod cycle and identical husbandry and feeding) for six weeks before the collection of the blood samples. The measurement of the total ALP and serum minerals was performed with automated biochemistry analysers using the BioMérieux kits, the serum electrolyte Ca(2+) Diametrics Medical, Inc specific cassettes and the BALP and OC METRATM kits from QUIDEL Corporation. The mean +/- standard deviation values obtained were: total ALP 90.17 +/- 85.72 U/L, BALP 15.0 +/- 5.44 U/L, ratio BALP/ total ALP 29.28 +/- 24.22, OC 13.02 +/- 1.87 ng/mL, Ca 2.57 +/- 0.37 mmol/L, P 2.13 +/- 0.42 mmol/L, Mg 1.04 +/- 0.13 mmol/L, Ca(2+) 1.29 +/- 0.04 mmol/L. Significant correlations were observed between the total ALP and Ca (r = 0.5939; P = 0.05) and OC and Ca (r = 0.5706; P = 0.05). Reference to the serum values of bone turnover parameters in sheep could be of great value in research and could provide complementary non-invasive information on the bone healing process, particularly with regard to obtaining an early prognosis of fracture healing.

Comparison of rat and human alkaline phosphatase isoenzymes and isoforms using HPLC and electrophoresis

Total activity of alkaline phosphatase (ALP) in serum represents the sum of activities of some isoenzymes and their numerous isoforms derived from various tissues of the organism. The aim of this work was to separate ALP isoenzymes and their isoforms in rat and human serum, compare the properties of serum ALP isoforms in rats and humans, and determine the usefulness of some analytical methods for specific measurements of ALP isoenzyme and isoform activities. Two methods of separation, i.e. high-performance liquid chromatography (HPLC) and agarose gel electrophoresis were chosen. The combination of HPLC with electrophoresis of the eluted fractions and with ALP inhibition methods (urea, l-phenylalanine), inactivation (heat) and precipitation (wheat-germ lectins) enabled the identification of isoenzymes and isoforms of ALP in serum. Using chromatography and a post-column reactor, three isoforms of the intestinal isoenzyme and one bone isoform of a tissue non-specific isoenzyme were detected. Rat serum differs significantly from human as regards activities of intestinal and hepatic isoforms, whereas the properties of the bone isoform are similar in both species. Our HPLC method offers a higher resolution than agarose gel electrophoresis with respect to ALP subfractions in rat serum.

Convenient Procedures for Human Hair Protein Films and Properties of Alkaline Phosphatase Incorporated in the Film

We have developed a novel method of extracting proteins from human hair in the absence of detergent called the "Shindai Method". Using the protein solution consisting of hard alpha-keratins and matrix proteins prepared by this method, we developed two procedures for preparing hair protein films. The protein solution was mixed with trichloroacetic acid (TCA), perchloric acid (PCA) or guanidine-HCl (GHA), and then exposed in distilled water. Light brown aggregates immediately formed (Pre-cast method). The other method is based on the same characteristics of the hair proteins to form protein aggregates. The protein was directly exposed to the solution containing TCA, PCA, GHA, HCl, H(2)SO(4) or acetate buffer (Post-cast method). The maximum yield was greater than 70%. These protein films were water-insoluble and mainly made up of alpha-keratins. Scanning electron micrographs showed that the fine surface of the protein films was composed of particles, filaments, and porous structures and the constitution was dependent on the preparation procedure used. When porcine intestine alkaline phosphatase (ALP) was mixed with the hair protein solution in a Post-cast method using acetate buffer (pH 5), ALP was incorporated into the alpha-keratin films. The activity retained in the protein film was approximately 8% of the original level. The biochemical properties of the ALP activity in the film were similar to those of the native enzyme.

Diagnosis and Monitoring of Hepatic Injury. I. Performance Characteristics of Laboratory Tests

Purpose: To review information on performance characteristics for tests that are commonly used to identify acute and chronic hepatic injury.

Data Sources and Study Selection: A MEDLINE search was performed for key words related to hepatic tests, including quality specifications, aminotransferases, alkaline phosphatase, γ-glutamyltransferase, bilirubin, albumin, ammonia, and viral markers. Abstracts were reviewed, and articles discussing performance of laboratory tests were selected for review. Additional articles were selected from the references.

Guideline Preparation and Review: Drafts of the guidelines were posted on the Internet, presented at the AACC Annual Meeting in 1999, and reviewed by experts. Areas requiring further amplification or literature review were identified for further analysis. Specific recommendations were made based on analysis of published data and evaluated for strength of evidence and clinical impact. The drafts were also reviewed by the Practice Guidelines Committee of the American Association for the Study of Liver Diseases and approved by the committee and the Association’s Council.

Recommendations: Although many specific recommendations are made in the guidelines, some summary recommendations are discussed here. Alanine aminotransferase is the most important test for recognition of acute and chronic hepatic injury. Performance goals should aim for total error of <10% at the upper reference limit to meet clinical needs in monitoring patients with chronic hepatic injury. Laboratories should have age-adjusted reference limits for enzymes in children, and gender-adjusted reference limits for aminotransferases, γ-glutamyltransferase, and total bilirubin in adults. The international normalized ratio should not be the sole method for reporting results of prothrombin time in liver disease; additional research is needed to determine the reporting mechanism that best correlates with functional impairment. Harmonization is needed for alanine aminotransferase activity, and improved standardization for hepatitis C viral RNA measurements.

Physiologic concentrations of bile salts inhibit rat hepatic alkaline phosphatase but not the intestinal isoenzyme

OBJECTIVE

The effect of bile salts on alkaline phosphatase (EC 3.1.3.1) activity from Wistar rat liver, duodenum, jejunum, and serum was investigated.

DESIGN AND RESULTS

For concentrations higher than 1 mM conjugated bile salts (glycocholate, glycochenodeoxycholate, taurocholate, taurodeoxycholate, and taurochenodeoxycholate) inhibited hepatic ALP but, up to concentrations of 10 mM, had no effect on intestinal ALP. Also cholate, deoxycholate, and chenodeoxycholate, within the same concentration range, did not have any effect on intestinal ALP. ALP inhibition induced by conjugated bile salts was significantly higher in serum of starved rats than in serum of fed animals, what is in good agreement with the known higher proportion of hepatic ALP and lower proportion of intestinal ALP in serum of starved rats.

CONCLUSIONS

Bile salts can, thus, be used to help discriminating between tissue-nonspecific and intestinal ALP isoenzymes and identifying pathologic conditions where the relative quantities of these isoenzymes are altered in serum. Inhibition of hepatic ALP by physiologic concentrations of bile salts may bear some relation to the bile salts effects on their own enterohepatic circulation and/or biosynthesis.

Importance of assay conditions in visualization and quantitation of serum alkaline phosphatase isoenzymes separated by electrophoresis

The importance of separation and identification of serum alkaline phosphatase (ALP; E.C. 3.1.3.1) fractions/isoenzymes has been frequently reported. Each serum ALP fraction/isoenzyme quantitation has both practical and theoretical importance. In the present work, serum was collected from Wistar rats and, in identical experimental conditions, total serum ALP activity and serum ALP electrophoretic fractions/isoenzymes activities were quantified. Different results for both kinds of ALP activity were obtained when different buffers or mixture of these buffers (carbonate/bicarbonate; 2-amino-2-methyl-1-propanol/HCl; Veronal, sodium diethylbarbiturate/HCl), pH conditions (9.4 and 10.4) and substrates (alpha- and beta-naphthyl phosphates) were used. Higher total serum ALP activity was always observed with beta-naphthyl phosphate, independently of the buffer (or mixture of buffers) and pH used. Electrophoresis allowed the separation of two serum ALP fractions. Activity of both serum ALP electrophoretic fractions was always higher with beta-naphthyl phosphate, except with carbonate/bicarbonate pH 10.4. The effect of a change in pH was buffer- (or mixture of buffers) and substrate-dependent; the addition of a second buffer (to that previously used) was not always accompanied by an increase or decrease (of the same magnitude) in our results. The results obtained with different buffers (or mixture of buffers) were not identical with substrates and pH values. It is concluded that (i) from the same electrophoretic separation of serum ALP fractions/isoenzymes, different values for its activity can be obtained by changing the assay conditions used for ALP visualization (revelation, staining); (ii) the same assay conditions for quantitation of total serum ALP and serum ALP electrophoretic fractions/isoenzymes should be used; (iii) the choice of assay conditions should take into account the biochemical problem being studied in each case.

Basic principles and clinical applications of biochemical markers of bone metabolism: biochemical and technical aspects

The interest in and the need for effective measures to be used in the screening, diagnosis, and follow-up of disorders of connective tissue, bone, and mineral metabolism has markedly grown. Next to clinical and imaging techniques, indices of bone turnover have come to play an important role in the assessment of metabolic bone disease. In osteoporosis, recent research has shown that bone markers may also be used to predict future bone loss and hip fractures (in larger cohorts of older patients), identify individuals at risk for osteoporosis, select therapy, and predict and monitor the therapeutic response in individual patients. The development of new markers of bone metabolism has greatly enriched the spectrum of serum and urine analytes used in the assessment of skeletal pathologies. Besides total alkaline phosphatase, other markers such as bone-specific alkaline phosphatase, osteocalcin, or the collagen propeptides are being used to measure bone formation. Bone resorption, previously assessed only by the measurement of urinary calcium and hydroxyproline, may now be detected more precisely by a number of new serum and urine markers. Among these, the pyridinium crosslinks and the telopeptides of collagen type I are presently considered the most specific markers of bone resorption. More recently, bone sialoprotein has also been suggested as a marker of bone resorption in serum. Tartrate-resistant acid phosphatase is now measurable by immunoassay. This article surveys the biochemistry and relevant technical aspects of the currently available markers of bone metabolism.

Rat serum alkaline phosphatase electrophoretic fractions: variations with feeding, starvation and cellulose fibre ingestion

The effect of feeding, starvation and fibre ingestion on alkaline phosphatase (ALP) activity (E.C. 3.1.3.1) was studied in Wistar rat serum. Using identical assay conditions for total ALP activity determination and for electrophoretic ALP isoenzymes/fractions activity calculation, alpha- and beta-naphthyl phosphates and p-nitrophenyl phosphate were used as substrates and 2-amino-2-methyl-1-propanol/HCI was used as buffer, respectively. Total activity with beta-naphthyl phosphate was significantly higher than with alpha-naphthyl phosphate and p-nitrophenyl phosphate; with alpha-naphthyl phosphate it was significantly higher than with p-nitrophenyl phosphate. With all substrates, fed animals had significantly higher total activity than starving ones. Electrophoresis allowed the separation of two fractions. The second fraction activity was significantly higher in the fed group than in the starving ones, irrespective of the substrate used. Starving animals with fibre showed higher values of this fraction than starving animals without fibre, the difference reaching statistical significance with alpha-naphthyl phosphate. The first fraction predominated in both starved groups and the second in the fed group. The second fraction was identified as intestinal ALP. We conclude that the mechanical stimulation of the digestive tract appears to influence the passage of intestinal ALP to serum. The experimental conditions used enable quantification of electrophoretic fractions based on total activity. Activity depends on the substrate used.

The bone isoenzyme of alkaline phosphatase in hypercalcaemic cancer patients

Alkaline phosphatase (AP) is the classic marker of bone formation, especially in cancer patients, but the interpretation of its measurement is complicated by the existence of various circulating isoenzymes, especially of liver origin. The introduction of a mass measurement of the bone isoenzyme of AP (BAP) by an immunoradiometric assay has markedly improved the sensitivity and the specificity of the determination. We measured BAP and other markers of bone turnover in 46 patients with tumour-induced hypercalcaemia (TIH), which is an interesting model for evaluating markers of bone formation because of the uncoupling between bone formation and bone resorption found by histomorphometric techniques. The extent of bone metastatic involvement was evaluated by planimetry on bone scintigraphy. Mean (+/- S.D.) BAP concentrations were slightly higher in patients with TIH than in healthy subjects, 15.5 +/- 8.5 versus 12.4 +/- 3.5 micrograms/L (P < 0.05). However, the scatter of the data in TIH patients was quite marked. Increased values (10/46 patients, 22%) occurred only in patients with bone metastases. Total AP, gamma GT and BGP levels, as well as markers of bone resorption, were not significantly different between patients with or without bone metastases. BAP levels were significantly correlated with AP (rs = 0.63; P < 0.01) but not with BGP levels nor with markers of bone resorption. BAP levels were also correlated with the extent of bone uptake at scintigraphy (rs = 0.54; P < 0.01), but this was not the case for total AP or BGP. In the 36 patients re-evaluated when normocalcemic after pamidronate therapy, BAP levels increased from 16.3 +/- 9.2 to 22.2 +/- 21.3 micrograms/L (P < 0.05) but there were no significant changes in AP or BGP concentrations. In summary, our data confirm the existence of an uncoupling in bone turnover in TIH and indicate that cancer hypercalcaemia is another pathological condition characterised by a discordance between BAP and BGP concentrations. BAP levels appear to be a better reflection of bone metastatic involvement than total AP or BGP and their short-term increase after pamidronate therapy could reflect the recently described effects of bisphosphonates on osteoblasts.

Assessment of the performance of a capture immunoassay for the bone isoform of alkaline phosphatase in serum

We report the analytical validation of an immunocapture assay for the bone isoform of alkaline phosphatase in serum. A between batch imprecision of less than 10% was found, being about 8% at the upper limit of the reference range, and with a detection limit of 0.8 IU/l at 37 degrees C. The crossreactivity of the method with the liver isoform was found to be in the range of 3-13% depending on the method employed. Unexpectedly the correlation of results with a non-immunological method for the quantitation of bone ALP showed significant differences between samples from children and patients with Paget's disease, with an apparent lower level of capture in the case of children. These data suggest that there may be differences in the epitope recognised by the antibody, which may be due to the presence of different forms of bone enzyme in these two populations. The significance of these observations is not clear at this stage.

Reaction of the coordinate complexes of inositol hexaphosphate with first row transition series cations and Cd(II) with calf intestinal alkaline phosphatase

The reaction of alkaline phosphatase (APase) with the complexes of myo-inositol hexakisphosphate (IHP) and various cations at pH 7.2 results in a decrease in activity. Singly, neither IHP nor metal ions induce such changes. IHP-Mn(II) complexes were the least effective. Using the ions of nickel or cadmium, activity was reduced by > 95%. A similar large decrease (> 99%) was seen previously in the reaction of APase with IHP-Cu(II) complexes. With Co(II) and IHP as reactants, the activity was reduced to 10-12% of that of the native enzyme. When the apoprotein, prepared by reaction of the enzyme with either EDTA or 1,10-phenanthroline, was titrated with Co(II), the activity was equal to that resulting from the reaction of the enzyme with IHP-Co(II) complexes. Titration with zinc restored 95% of the original activity. The products are metal-substituted derivatives in which the resident catalytic (A-site) zinc ions, at least, are replaced by the cation of the IHP complex that was used. The rates of such reactions were fastest with the complexes of Cu(II) and Cd(II) (0.12 min-1), less so with Co(II) as the ion (0.056 min-1), and slowest with complexes of nickel and manganese (0.01 min-1). In every case, the rate of reaction, but not its extent of change, was inhibited by zinc ions that reduced rate constants to 0.0014-0.0054 min-1. Magnesium ions had no effect. Likewise, Mn(II), with but one exception, did not affect the reactions. When present along with IHP-Ni(II) complexes, the rate was increased and the enzyme activity further decreased. If Zn(II) was also present, this enhancement was eliminated. All changes in enzyme activity were reversible by treatment with EDTA followed by reconstitution with zinc. Approximately 95% conversion to the original activity could be attained. Reactivation of modified APase preparation also could be attained, in some cases, by pre-incubation with Zn(II) at pH 8. For example, conversion of the Cd(II)-substituted APase to the zinc enzyme was rapid and complete in 15 min. With the Cu(II)-substituted derivative, reactivation was much slower. Incubation with zinc ions had little or no effect on other Me(II)-substituted APase preparations. Co-APase and Cu-APase, prepared from the apoprotein, behaved similarly to their respective "counterpart product" of the appropriate metal ion-exchange reaction. In contrast, Co-APase, but not Cu-APase, could be converted to the zinc enzyme by incubation with IHP-Zn(II) complexes at pH 7.2. The reaction rate of the various metal-substituted APase preparations with EDTA varied with the IHP-Me(II) used in its formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Interpretation and clinical significance of alkaline phosphatase isoenzyme patterns

Alkaline phosphatase (ALP, EC 3.1.3.1) is a membrane-bound metalloenzyme that consists of a group of true isoenzymes, all glycoproteins, encoded for by at least four different gene loci: tissue-nonspecific, intestinal, placental, and germ-cell ALP. Through posttranslational modifications of the tissue-nonspecific gene, for example, through differences in carbohydrate composition, bone and liver ALP are formed. Nowadays, most commercially available methods for separating or measuring ALP isoenzymes are easy to perform and sensitive and allow for reproducible and quantitative results. As more isoenzymes and isoforms have been characterized, confusion has arisen due to the many different names they were given. For the sake of simplicity and because of structural analogies, we propose an alternative nomenclature for the ALP isoenzymes and isoforms based on their structural characteristics: soluble, dimeric (Sol), anchor-bearing (Anch), and membrane-bound (Mem) liver, bone, intestinal, and placental ALP. Together with lipoprotein-bound liver ALP and immunoglobulin-bound ALP, these names largely fit the many forms of ALP one can encounter in human serum and tissues. The clinically relevant isoenzymes are sol-liver, Mem-liver, lipoprotein-bound liver, and Sol-intestinal ALP in liver diseases, and Sol-bone and Anch-bone ALP in bone diseases. Many different isoenzyme patterns can be found in malignancies and renal diseases. This test provides the clinician with valuable information for diagnostic purposes as well as for follow-up of patients and monitoring of treatment. However, ALP isoenzyme determination will only provide clinically useful information if the patterns are correctly interpreted. In this respect, care should be taken to use the proper reference ranges, taking into account the age and sex of the patient. A normal total ALP activity does not rule out the presence of an abnormal isoenzyme pattern, particularly in children. Separating ALP into its isoenzymes adds considerable value to the mere assay of total ALP activity.

Determination of alkaline phosphatase isoenzymes in serum by high-performance liquid chromatography with post-column reaction detection

A weak anion-exchange high-performance liquid chromatographic procedure with post-column reaction detection for simultaneous determination of alkaline phosphatase (EC 3.1.3.1, ALP) isoenzymes is described. We identified six peaks with ALP isoenzyme activity in normal serum. The peaks were, in order of elution, one intestinal/bone, two bone and three liver ALP isoenzymes. This new assay with automatic injection, on-line post-column reaction detection and powerful integration data system could be of significant value in the routine clinical biochemistry laboratory. The advantages include improved sensitivity and selectivity over previous methods for the determination of ALP isoenzymes.

Alkaline phosphatase and phosphoamino acid phosphatases in normal and cancerous tissues of the human larynx

The activities of alkaline phosphatase and phosphoamino acid phosphatases were measured in normal and cancerous regions of the human larynx. For each larynx, alkaline phosphatase and phosphotyrosine phosphatase activities were higher in the tumor than in the corresponding normal tissue. Phosphothreonine and phosphoserine phosphatase activities were relatively low and there were no consistent trends. The increased alkaline phosphatase activity in the tumors supports histological observations that ossification of cartilage seems to occur at the site of invasion; the phosphatase acting on phosphotyrosine could serve as a regulator of cell differentiation during tumorigenesis.

Familial increased serum intestinal alkaline phosphatase: a new variant associated with Gilbert's syndrome

Investigation of mild, inherited increased serum alkaline phosphatase activity partially combined with Gilbert's syndrome in one family showed, apart from a normal liver fraction, an intestinal isoenzyme pattern and an extra band in the agar electrophoresis. Analysis by agarose electrophoresis before and after incubation of neuraminidase showed that the extra fraction was an intestinal variant isoenzyme. The precise genetic background of the two disorders in this family could not be determined from the available data. Abnormal activities of (regular) intestinal alkaline phosphatase isoenzyme caused the increase in serum alkaline phosphatase in the absence of disease.

Electron-cytochemical localization of alkaline phosphatase to G cells of Necturus maculosus antrum

Electron-cytochemical localization of alkaline phosphatase activity was performed on G cells of Necturus maculosus antral mucosa. Alkaline phosphatase activity was localized to the nuclear membrane, the Golgi/endoplasmic reticulum, and the limiting membranes of G cell peptide-secretion vesicles. There was no specific localization of alkaline phosphatase activity to the plasma membrane. Treatment of the tissues with levamisole (an alkaline phosphatase inhibitor) did not markedly reduce the specific alkaline phosphatase activity. Specific lead deposition was reduced by removal of the substrate from the reaction mixture. The results from this study on N. maculosus G cells demonstrate that alkaline phosphatase activity can be found in a non-mammalian gastric endocrine cell and that specific activity was localized primarily to those intracellular structures involved with protein biosynthesis.

Detection of macroenzymes in serum by high-performance gel permeation chromatography

A rapid high-performance gel permeation chromatographic method to confirm the presence of enzymes with abnormally high relative molecular masses (macroenzymes) in serum is described. The technique requires 200 microliters of serum, can be automated and has been implemented for the analysis of creatine kinase (CK), lactate dehydrogenase, amylase, and alkaline phosphatase (ALP) activities. Serum fractionation according to relative molecular mass is completed within 21 min, and 84-106% of enzyme activities are recovered in the eluted fractions. The elution patterns obtained make possible the differentiation of 40 samples containing at least 10 U/l immunoglobulin-enzyme complexes, aggregated mitochondrial CK or membrane fragments carrying ALP activity from 40 control samples without these high-mass enzyme forms.

Correlation between alkaline and acid phosphatase activities and age-related osteopenia in murine vertebrae

Lumbar vertebrae (L4) from CW-1 female mice were examined for age-related changes in alkaline and acid phosphatase activities from young to old age. Histochemically, both enzymes were encountered along the bony surfaces of both trabecular and cortical bones with no significant age-related changes in their distribution. Biochemical determinations of bone alkaline phosphatase (Alk'ase) activity revealed that for a given unit level of bone or the bone as a whole no significant changes took place, whereas acid phosphatase (Acid'ase) activity was found to have increased significantly with age. A high positive correlative relationship was noted between the calcium content and the trabecular bone volume of the same vertebrae. It may, therefore, be proposed that age-related bone loss in mice could be attributed to an enhanced resorption rather than to a substantial reduction in the formative potential of bone cells.

Clinical use of serum enzymes in liver disease

Some of the many enzymes found in hepatocytes can be measured in the serum and are used as tests of liver function. We now review the current knowledge of their physiology and pathophysiology and outline their clinical usefulness. We divide them into two categories: enzymes that primarily reflect cholestasis, such as the alkaline phosphatase, the 5'-nucleotidase, and the gamma-glutamyl transpeptidase, and those that primarily reflect hepatocellular necrosis, such as the aminotransferases. We also briefly discuss several enzymes of more limited usefulness.

Tissue activities of enzymes of diagnostic interest in the marmoset and rat

The activities of enzymes of diagnostic interest were investigated in the liver, heart, kidney and muscle of the marmoset (Callithrix jacchus) and the rat. Methods of tissue extraction which gave maximal enzyme activity were used and comparison between the species showed some major differences. AST, LDH and GDH showed a similar distribution in both species but ICDH activity was much higher in the rat heart than in any other rat or marmoset organ. ALP, LAP and GGT were present in much higher activities in the rat kidney than in the marmoset kidney, a finding which was reversed in the liver of these animals. The major ALT-containing organ in the rat was the liver but, in the marmoset, this enzyme was found in relatively large quantities in the heart and muscle also. These differences can be of importance when plasma enzyme activities are measured following tissue damage.

Isoelectric focusing on cellulose acetate membrane: a separation procedure for alkaline phosphatase isoenzymes

An isoelectric focusing technique for the separation of alkaline phosphatase isoenzymes on cellulose acetate membrane is described. Optimal conditions for isoelectric focusing were established by changing ampholine concentration and focusing conditions. Bone, liver, intestinal, and placental isoenzymes can be resolved into various sub-bands in a pH range of 4.1 to 5.2. These sub-bands were correlated with the findings of electrophoretic isoenzyme separation. The whole procedure proves very simple to perform and comparatively time saving (4 h). This procedure may help clarify the problems of ALP isoenzyme differentiation when electrophoretic patterns are unresolved.

Framework invasion by laryngeal carcinoma

Invasion of the laryngeal framework by cancer implies a tumor that has spread beyond the bounds of the organ of origin, which may affect the outcome of the disease. Framework invasion almost invariably takes place in ossified or calcified cartilage, and the reason for this has never before been adequately explained. The finding of increased density on some computerized tomography scans where the tumor was invading the framework stimulated this study of the mechanisms of this type of spread. One hundred fifty-eight consecutive laryngeal specimens were examined by a serial sectioning method to elucidate this. Several laryngeal specimens were examined for alkaline phosphatase in the tissues, and two specimens were examined for collagenase. A method of tetracycline labeling was used to measure the amount of osteoblastic activity in another two specimens. Framework invasion occurred mainly at the glottic level and exclusively in ossified or calcified cartilage. This type of invasion was associated with osteoblastic activity which appeared to be at least partially mediated by tumor-produced alkaline phosphatase. Osteoclastic activity took place hand-in-hand with the former process, and at this stage, tumor remained outside the perichondrium. Tetracycline labeling confirmed active bone deposition in these areas and appeared to explain the finding of increased ossification seen on computerized tomography scans where early invasion was taking place.

Enzymatic activities in the iris-ciliary body of the rabbit eye during experimentally induced acute ocular inflammation

Intravitreal injection of 5 micrograms of Shigella endotoxin, in the rabbit eye, induced an acute inflammatory response which was characterised by conjunctival hyperaemia, limbal and ciliary vascular injection, iritis, aqueous flare, miosis and reduction in intraocular pressure. Iris-ciliary body tissues, from normal and inflamed eyes, were fractionated into subcellular enriched fractions and the activities and distribution of selected enzymes were estimated. Alkaline phosphatase, a plasma membrane-bound enzyme, showed an increase in activity, whereas succinate dehydrogenase and Mn-Superoxide dismutase, both mitochondrial-bound enzymes, exhibited decreased activities. Lysosomal acid phosphatase displayed an increase in free activity and retention of latent activity inside the organelle. No alteration in free activity was shown by acid cathepsin. The cholinesterases did not exhibit any changes in activities nor did the cytosolic enzymes Cu/Zn-superoxide dismutase and lactate dehydrogenase. The decrease activity of the respiratory mitochondrial enzyme succinate dehydrogenase may contribute to the reduction in intraocular pressure, and the ability of the lysosomal organelles to retain their hydrolytic enzymes, ensures recovery of the cell from acute inflammatory attack.

Molecular nature of three liver alkaline phosphatases detected by drug administration in vivo: differences between soluble and membranous enzymes

1. Activities of alkaline phosphatase, liver-membranous, liver-soluble and serum-soluble, were dramatically induced in dogs by treatment with both phenobarbital and brovanexine. The treatment induced a 17-fold increase in membranous, a 155-fold increase in soluble, and a 105-fold increase in serum alkaline phosphatases. 2. There was no difference in the enzymatic behavior of the three forms of alkaline phosphatase, on heat stability, amino acid inhibition and optimum pH. 3. When the three alkaline phosphatases were treated initially with n-butanol, their apparent molecular size was identical. After treatment with phosphatidylinositol-specific phospholipase C, the liver-soluble and serum-soluble alkaline phosphatase were of the same molecular size. Liver-membranous alkaline phosphatase, however, was larger in molecular size than the other two forms, suggesting a difference between soluble and membranous alkaline phosphatase forms. 4. In terms of the sugar moiety of the three alkaline phosphatase forms, the membranous enzyme showed more of the higher affinity fraction and less of the lower affinity fraction of concanavalin A, compared with the soluble enzymes. 5. Consequently, it is possible that the membranous enzyme may be solubilized by an enzyme such as phosphatidylinositol-specific phospholipase C and modify further the sugar moiety of alkaline phosphatase molecules, resulting in serum alkaline phosphatase transfer from the soluble enzyme in liver.

Alkaline phosphatase and cholestasis

The process of cholestasis in both man and rat leads in the majority of cases to the appearance of a biliary band in the electrophoresis of alkaline phosphatase isoenzymes. In this article, the biochemical nature and mode of formation of the biliary band is discussed, with reference to its appearance in cholestasis and other hepatobiliary diseases.

Hydrophobic properties of alkaline phosphatases

The butanol extraction method of Morton (1950), a routine step in enzyme purification, is discussed with special reference to a hydrophobic form of alkaline phosphatase from human liver tissue. This form slowly precipitates from butanol-extracted liver tissue homogenates stored at 4 degrees C. Furthermore, it is lost when acetone precipitation is applied as a purification procedure. The soluble form in liver tissue is shown to have a higher relative hydrophobicity than the serum liver/bone isoenzyme. The use of sodium cholate in the isolation of the hydrophobic form produces an artefact in isoelectric focusing, which can be abolished by dialysis prior to focusing.

Changes in alkaline-phosphatase isoenzymes of hard tissue origin during facial development in the rat

Non-specific alkaline phosphatase (APase) activity was demonstrated histochemically in the hard-tissue-forming areas of the developing rat face from the 14th embryonic day. Isoenzyme distribution of APase was recorded by isoelectric focusing. Three APase isoenzyme bands with lower isoelectric points than adult forms were recorded. Inhibition studies with levamisole dexamisole, L-p-bromotetramisole, D-p-bromotetramisole, diphosphonates and urea showed the embryonic isoenzymes to have the same sensitivity as the adult forms except to urea. Heated to 56 degrees C, both embryonic and adult APase were rapidly inactivated. The differences between the embryonic and adult forms of APase may represent the expression of different gene loci or a difference in post-translational modification.