Aminotransferase activity

FIGURE 14.26 (a) Antigen used to create an abzyme with aminotransferase activity, (b) Aminotransferase reaction catalyzed by the abzyme. 

Practical conversion from ACA to L-phenylalanine was best achieved when acylase and aminotransferase activities were equal. This could be achieved by using 10 gram B. sphaericus and 25 gram P. denitrificam per litre medium. 

Rej. R. and Vanderlinde, R. E. Effects of buffers on asperate aminotransferase activity and association of the enzyme with pyridoxal phosphate. Clin. Chem. (1975), 21, 1585-1591. 

Palaiologos, G., Hertz, L. and Schousboe, A. Evidence that aspartate aminotransferase activity and ketodicarboxylate carrier function are essential for biosynthesis of transmitter glutamate. /. Neurochem. 51 317-320,1988. 

The investigation of the aminotransferase activity of apple ACS carried out by Feng et al reveals that it is able to reductively aminate PLP to PMP by transamination of some L-amino acids to their corresponding a-keto acids. The enzyme has shown substrate specificity with the preference of Ala > Arg > Phe > Asp. The addition of excess pyruvate causes a conversion of the PMP form of the enzyme back to the PLP form. The quite unstable PMP form of ACS can generate apoenzyme, which captures PLP to restore its physiologically active form. 

Except the aminotransferase activity of AT-ACSlO and 12 isozymes, shown in heterologous nonplant systems, the catalytical status of a majority of members of AT-like enzymes is still unknown. The only exception is RH-ACS, whose expression has been evidenced to increase dramatically and correlate with ethylene levels in senescing petals of Rosa hyhrida Moreover, the investigation carried out by Barnes et on Pta-ACSl from conifers suggests the putative ACS activity of this isozyme. 

This enzyme [EC 5.1.1.15], also referred to as 2-amino-hexano-6-lactam racemase, catalyzes the reversible interconversion of the L- and D-stereoisomers of 2-amino-hexano-6-lactam. The enzyme, which utilizes pyridoxal phosphate, will also catalyze the interconversion of 2-aminopentano-5-lactam and 2-amino-3-mercaptohex-ano-6-lactam. The enzyme exhibits a minor aminotransferase activity with certain a-amino acids. 

Intramuscular injections have been shown to produce elevations in serum enzyme activities presumably due to either inflammatory areas in the muscle or actual breakdown of cells and release of enzyme. In one study, preinjection values of creatine phosphokinase were in the normal range of 24-100 units. Multiple intramuscular injections of penicillin, diuretics, and narcotics every 6 hours caused the creatine phosphokinase values to rise to levels between 160 to 240 units, or up to 2.5 times the upper limit of normal. When the injections were stopped, the creatine phosphokinase values returned to normal within 48 hours (B7). Similar observations of aspartate aminotransferase activities were made in patients receiving intramuscular injections of penicillin every 4 hours. Activities rose to values as high as 200 units. Other workers have reported injection related serum creatine phosphokinase elevations following intramuscular administration of chlorpromazine and suxamethonium (HIO, M11,T6). 

Addition of ethyl acetate to a specimen having a transaminase activity of 47 units was responsible for the following increases in enzyme activity 10 mg/100 ml, 60 units 20 mg/100 ml, 77 units 40 mg/100 ml, 107 units and 80 mg/100 ml, 150 units. Transaminase activity in these specimens determined by another method ranged from 32 to 34 units (C7). Thus, when serum from patients with ketosis is assayed for aspartate aminotransferase activity by the diazo method, false elevations of activity may be recorded due to reaction of acetoacetic acid. In Table 11 are shown some values obtained by the diazo method and by an ultraviolet NADH NAD aspartate aminotransferase technique (B12). Examination of the medical records of these patients indicated that they were either diabetics who were in ketosis or individuals who were eating very poorly and had some degree of starvation ketosis. Similar elevations have been observed in patients receiving p-aminosalicylic acid (G6). 

In the same study, serum biochemical parameters (aspartate aminotransferase activity and total bilirubin) were increased at doses of 20 mg/kg/day. Urinary excretion of coproporphyrin increased at dose levels of 20 mg/kg/day in lifetime studies however, histopathological lesions were not found (Kociba et al. 1977a). 

A similar activity level was obtained in the deoxycholate, Triton X-100, and NP-40 extract preparations. Octyl glucoside and CHAPS extract preparations showed no detectable prephenate aminotransferase activity. When the hemoglobin step was used, there was no increase in the soluble activity recovered in the initial supernatant fraction, but the specific activity of the deoxycholate (the only detergent tried in this experiment) extract increased about tenfold. We would anticipate equally good results with use of Triton X-100 or NP-40 in combination with the hemoglobin step. 

Some cases of hepatotoxicity have been reported to be associated with exposure to coumarin. One possible case was reported by Beinssen (1994) and six by Loprinzi et al. (1997). Marshall et al. (1994) reported one case in which elevated serum aminotransferase levels were measured in a patient given 5 g coumarin per day. In two lymphoedema patients given 90 mg coumarin per day for five months, Koch et al. (1997) reported elevated serum alanine aminotransferase activity. Faurschou (1982) reported a case of toxic hepatitis in a patient given coumarin daily for eight weeks, which was characterized by hepatomegaly and elevated serum enzyme levels. All signs of liver toxicity returned to normal on cessation of treatment. 

Cottrell et al. (1996) reported that a single oral dose of coumarin produced liver necrosis in mice 200 mg/kg bw coumarin was hepatotoxic to both C3H/He and DBA/2 mice. Hepatotoxicity was characterized by an increase in plasma aminotransferase activity, mild subcapsular linear hepatocyte necrosis and, in some C3H/He mice, centrilobular necrosis. Mice were pretreated with (3-naphthoflavone (80 mg/kg bw), Aroclor 1254 (54, 125 or 162 mg/kg bw) or vehicle alone by intraperitoneal injection for three consecutive days. Twenty-four hours later, a single dose of coumarin (200 mg/kg bw) or vehicle was administered by gavage. Pretreatment with... 

Naltrexone is generally taken once a day in an oral dose of 50 mg for treatment of alcoholism. An extended-release formulation administered as an IM injection once every 4 weeks is also effective. The drug can cause dose-dependent hepatotoxicity and should be used with caution in patients with evidence of mild abnormalities in serum aminotransferase activity. The combination of naltrexone plus disulfiram should be avoided, since both drugs are potential hepatotoxins. Administration of naltrexone to patients who are physically dependent on opioids precipitates an acute withdrawal syndrome, so patients must be opioid-free before initiating naltrexone therapy. Naltrexone also blocks the therapeutic effects of usual doses of opioids. 

Elevations of serum aminotransferase activity (up to three times normal) occur in some patients. This is often intermittent and usually not associated with other evidence of hepatic toxicity. Therapy may be continued in such patients in the absence of symptoms if aminotransferase levels are monitored and stable. In some patients, who may have underlying liver disease or a history of alcohol abuse, levels may exceed three times normal. This finding portends more severe hepatic toxicity. These patients may present with malaise, anorexia, and precipitous decreases in LDL. Medication should be discontinued immediately in these patients and in asymptomatic patients whose aminotransferase activity is persistently elevated to more than three times the upper limit of normal. These agents should be used with caution and in reduced dosage in patients with hepatic parenchymal disease, Asians, and the elderly. In general, aminotransferase activity should be measured at baseline, at 1-2 months, and then every 6-12 months (if stable). 

Oral treatment of adult female Sprague-Dawley rats with 425 mg/kg bw caprolactam 21 and 4 h before killing resulted in a significant increase in serum alanine aminotransferase activity (33%), while hepatic ornithine decarboxylase activity and cytochrome P450 content were not changed significantly (Kitchin Brown, 1989). 

A single oral dose (> 400 mg/kg bw) of 1,2-dichloroethane to B6C3Fj mice induced an elevation of alanine aminotransferase activity and an increase in relative liver weight, and some mortality occurred. The lowest intraperitoneal dose inducing an elevation of these enzy mes was 500 mg/kg bw intraperitoneal doses of up to 600 mg/kg bw did not kill any of the animals ( = 5). Inhalation exposure to 500 ppm [2000 mg/m ] for 4 h was hepatotoxic to some of the mice, while at 150 ppm [600 mg/m- ] no toxicity was observ ed. Relative kidney weight was elevated after 300 mg/kg bw orally, 400 mg/kg bw intraperitoneally and after a 4-h exposure to 500 ppm 1,2-dichloroethane (Storer et al., 1984). 

When 82.7 or 165.4 mg/kg bw 1,1,1-trichloroethane was administered to male Fischer 344/N rats by gavage once daily for 21 days, a decrease in the total urine output and an increase in the urinary alanine aminotransferase activity were observed at the high dose. However, no sign of hyaline nephropathy, or any other microscopic effect on the kidney, was observed (United States National Toxicology Program, 1996). 

Harrison et al. (1985, 1987) reported on two construction workers who were exposed to 2-nitropropane while applying epoxy resin coating. One man died 10 days after exposure from fulminant hepatitis, the other man had persistently elevated serum aminotransferase activity. Serum concentrations of 2-nitropropane on admission were 13 mg/L in the man who died and 8.5 mg/L in his co-worker. 

Treatment of male Charles-Foster rats with sublethal doses of xylene (0.2 mL of 5 mmol/L extra-pure xylene solution on alternate days for 30 days isomeric composition not indicated) resulted in slight increases of serum aspartate and alanine aminotransferase and alkaline phosphatase activities and bilirubin concentration (Rana Kumar, 1993). A slight increase in alanine aminotransferase activity was also observed after a 3.5-week treatment of male Wistar rats with zneto-xylene (800 mg/kg bw per day on five days per week, by gavage) (Elovaara et al., 1989). Inhalation exposure of C3H/HeJ mice to /jora-xylenc (1200 ppm [5200 mg/m ], 6 h per day for four days) did not affect the serum alanine or aspartate aminotransferase or lactate dehydrogenase activities, or bilirubin level (Selgrade et al., 1993). 

Measurement of Alanine Aminotransferase Activity The activity (reaction rate) of alanine aminotransferase is usually measured by including an excess of pure lactate dehydrogenase and NADH in the reaction system. The rate of alanine disappearance is equal to the rate of NADH disappearance measured spectrophotometrically. Explain how this assay works. 

Gentile S, Turco S, Guarino G, Sasso FC, Torella R. Aminotransferase activity and acarbose treatment in patients with type 2 diabetes. Diabetes Care 1999 22(7) 1217-8. 

Free amino acids are further catabolized into several volatile flavor compounds. However, the pathways involved are not fully known. A detailed summary of the various studies on the role of the catabolism of amino acids in cheese flavor development was published by Curtin and McSweeney (2004). Two major pathways have been suggested (1) aminotransferase or lyase activity and (2) deamination or decarboxylation. Aminotransferase activity results in the formation of a-ketoacids and glutamic acid. The a-ketoacids are further degraded to flavor compounds such as hydroxy acids, aldehydes, and carboxylic acids. a-Ketoacids from methionine, branched-chain amino acids (leucine, isoleucine, and valine), or aromatic amino acids (phenylalanine, tyrosine, and tryptophan) serve as the precursors to volatile flavor compounds (Yvon and Rijnen, 2001). Volatile sulfur compounds are primarily formed from methionine. Methanethiol, which at low concentrations, contributes to the characteristic flavor of Cheddar cheese, is formed from the catabolism of methionine (Curtin and McSweeney, 2004 Weimer et al., 1999). Furthermore, bacterial lyases also metabolize methionine to a-ketobutyrate, methanethiol, and ammonia (Tanaka et al., 1985). On catabolism by aminotransferase, aromatic amino acids yield volatile flavor compounds such as benzalde-hyde, phenylacetate, phenylethanol, phenyllactate, etc. Deamination reactions also result in a-ketoacids and ammonia, which add to the flavor of... 

Ondansetron generally does not cause severe toxicity. Headache and constipation are the most frequent adverse effects. Light-headedness, dizziness, and transient increases in serum aminotransferase activity can occur. Extrapyramidal effects have occurred rarely, and anaphylactoid reactions have been reported. 

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