Enzymes in diagnosis

Enzymes, especially those in the cytosol, may escape from a damaged or diseased cell and appear in the blood. Since 

The measurement of enzyme activities in tissues other than blood can also be carried out, for example, in extracts of tissue obtained by biopsy, from red or white blood cells or from cerebrospinal fluid. Such measurements are valuable in diagnosis of genetic diseases in 

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Assay of Enzymes In body fluids, enzyme levels aie measured to help in diagnosis and for monitoiing treatment of disease. Some enzymes or isoenzymes are predominant only in a particular tissue. When such tissues are damaged because of a disease, these enzymes or isoenzymes are Hberated and there is an increase in the level of the enzyme in the semm. Enzyme levels are deterrnined by the kinetic methods described, ie, the assays are set up so that the enzyme concentration is rate-limiting. The continuous flow analyzers, introduced in the early 1960s, solved the problem of the high workload of clinical laboratories. In this method, reaction velocity is measured rapidly the change in absorbance may be very small, but within the capabiUty of advanced kinetic analyzers. 

The detection of restriction fi agment length polymorphisms (RFLPs) facilitates prenatal detection of hereditary disorders such as sickle cell trait, beta-thalassemia, infant phenylketonuria, and Huntington s disease. Detection of RFLPs involves cleavage of double-stranded DNA by restriction endonucleases, which can detect subtle alterations in DNA that affect their recognized sites. Chapter 40 provides further details concerning the use of PCR and restriction enzymes for diagnosis. 

The diagnosis of PK deficiency depends on the determination of quantitative enzyme activity or qualitative abnormalities of the enzyme. In 1979, the International Committee for Standardization in Haematology (ICSH) established methods for the biochemical characterization of red blood cell PK variants (M22). Since the establishment of these methods, many PK-deficient cases have been characterized, including 13 cases of homozygous PK deficiency. Residual red blood cell PK activity is not usually associated with phenotypic severity,whereas enzymatic characteristics such as decreased substrate affinity, thermal instability, or impaired response to the allosteric activator fructose-1,6-diphosphate (F-1,6-DP) correspond to a more severe phenotype. 

Phenylalanine hydroxylase (PH) which requires tetrahydrobiopterin (BH4) as a cofactor, is defective in cases of phenylketonuria (PKU). This is a rare (prevalence 1 / 15 000 in the United Kingdom) genetic condition characterized by fair complexion, learning difficulties and mental impairment. If PH is either not present in the hepatocytes or is unable to bind BH4 and is therefore non functional, phenylalanine accumulates within the cells. Enzymes in minor pathways which are normally not very active metabolize phenylalanine ultimately to phenylpyruvate (i.e. a phenylketone). To use the traffic flow analogy introduced in Chapter 1, the main road is blocked so vehicles are forced along side roads. Phenylpyruvate is excreted in the urine (phenyl-ketone-uria), where it may be detected but a confirmatory blood test is required for a reliable diagnosis of PKU to be made. 

Measurement of the activities of some enzymes in blood this is one factor involved in the diagnosis of disease. 

Enzymes in clinical diagnosis ENZYMES IN CLINICAL DIAGNOSIS (p. 64)... 

There is no way of treating Tay-Sachs disease. Enzyme replacement is not considered a likely therapy because infused enzyme cannot penetrate the blood-brain barrier. However, the incidence of the disease has been dramatically decreased by prenatal diagnosis. Tay-Sachs disease is an autosomal recessive disease and so can arise only if both parents are carriers, i.e., if each parent carries a single defective gene for the hexosaminidase A enzyme. In that case there is a 25% chance that a child of these parents will have the disease. 

Another application of enzymes in the food industry is the separation of peroxidase (POD EC 1.11.1.7) from wasabi horseradish (Taniguchi et al., 1988). Using carbon dioxide, the enzyme was successfully separated from the flavor components so that the enzyme could be used as a label enzyme in clinical diagnosis and microanalysis with immunoassays, and the flavor components could be added to spices and foods. 

L15. Lott, J., Enzyme tests in gastroenterology. In Enzyme Tests in Diagnosis (D. W. Moss and S. Rosalki, eds.), pp. 60-89. Oxford University Press, New York, 1996. 

Nittner-Marszalska, M., Wojcicka-Kustrzeba, I., Bogacka, E., Patkowski, J., and Dobek, R. 2001. Skin prick test response to enzyme enolase of the baker s yeast (Saccharomyces cerevisiae) in diagnosis of respiratory allergy. Med Sci. Monit 7(1) 121-124. 

In recent years, the importance of enzyme levels in body fluids for clinical diagnosis has been recognized. It has been established that activities of secreted enzymes and cellular enzymes in serum are a sensitive indication of the pathophysiological condition of the body. Specific and sensitive substrates play a prominent role for this purpose. Fluorogenic substrates, e.g., enable sensitive micro-analyses. 

For practical purposes people frequently find it convenient to identify a normal range for a particular parameter. For example, clinically, we may measure all sorts of ions and enzymes in a patient s blood and then we want to be able to spot any abnormal values that may be of importance in diagnosis and treatment. To make it easier to spot these interesting values, clinicians like to establish a normal range for each substance measured. Then, all they have to do is check for values outside the official normal range. 

The diagnosis of G6PD deficiency is made by quantitative or semiquantitative assay. The methods used are based on the normal function of the G6PD enzyme in catalyzing the initial step in the pentose phosphate pathway (PPP). Screening tests depend on the inability of cells from deficient subjects to convert an oxidized substrate to a reduced state. The substrates... 

Prenatal diagnosis of I-cell disease has been based on greatly reduced phosphotransferase activity (cf. Biochemical Perspectives section) and abnormal intracellular-extracellular distribution of lysosomal enzymes in cultured amni-otic fluid cells (Table 17-3).As indicated in Table 17-3, amniotic fluid cells secrete large amounts of lysosomal enzymes into the extracellular medium. Decreased levels of lysosomal enzymes in chorionic villi obtained by biopsy have also been observed in I-cell disease however, the characteristic secondary effect (i.e.,increased levels of lysosomal enzymes in the extracellular compartment) is only partially expressed or not expressed at all in chorionic villi, suggesting an alternative mechanism for the transport of lysosomal proteins. Although... 

Table 17-3. Prenatal Diagnosis Levels of GlcNac-P04 Transferase and Various Lysosomal Enzymes in Amniotic Fluid and Cultivated Amniotic Fluid Cells...

The diagnosis of myocardial infarction is based on the patient s history, ECG changes and significant increases in myocardial enzymes. In particular there is a rise in cardiac creatine phosphokinase, reaching a peak 24 hours post infarction and an increase in troponin I and T, which are specific markers of myocardial injury when infarction has occurred. 

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