Creatinine iminohydrolase

For the diagnosis of kidney function, creatinine determinations in serum are increasing in popularity over urea measurements, since the creatinine level is not affected by a high protein diet or by metabolic rate, as is the case for urea. Enzymatic methods use either creatinine amido-hydrolase (EC 3.5.2.10) or creatinine iminohydrolase (EC 3.5.4.21) ... 

Danielsson (1982) proposed a reactor with immobilized creatinine iminohydrolase in a thermistor unit. Although the measuring range was 0.01—10 mmolA creatinine, the sensitivity was still too low for the assay... 

The very same enzymes have been combined by Mascini et al. (1985a) in an FIA system. Creatinine iminohydrolase was immobilized on the inner wall of nylon tubing (diameter 1 mm, length 1 m) and the ammonia liberated in the enzymatic reaction was measured with an NH3 electrode. Owing to the low sensitivity of the indicator electrode, the linear range was only 0.01-0.2 mmolA. 

Meyerhoff and Rechnitz (1976) developed a potentiometric creatinine sensor by inclusion of creatinine iminohydrolase between the gas-permeable membrane of an ammonia electrode and a dialysis membrane. Since the specific activity of the enzyme used was very low, 0.1 U/mg, only 43 mU could be entrapped at the electrode. Therefore the sensor was kinetically controlled and reacted to addition of the enzyme activator tripolyphosphate by an increase in sensitivity from 44 mV to 49 mV per concentration decade and a corresponding decrease of the detection limit. These effects agree with theoretical considerations of reaction-transport coupling. The samples were treated with a cation exchanger to remove endogenous serum ammonia. 

Plasma and urinary creatinine are commonly measured by the colorimetric alkaline picrate method of Jaffe or by alternative enzymatic methods. Enzymatic methods use creatinine amidohydrolase or creatinine iminohydrolase and are more specific for creatinine. The measurement of plasma creatinine may be affected by endogenous noncreatinine chromogens (e.g., bilirubin and ketones) this can overestimate plasma creatinine in dogs by up to 45% and to an even greater extent in rats... 

The second most common method used in automated analyzers is based on the use of enzymes to produce a compound that will react with a substance provided to form a colored product. For example, creatinine iminohydrolase (creatinine deiminase) catalyzes the conversion of creatinine to N-methyT hydantoin and ammonia. This reaction can be carried out in a flow injection analysis system setup so that the ammonia diffuses into an acceptor stream containing a pH indicator, the color changes of which are measured by diffuse reflectance. 

To create a potentiometric creatinine sensor, creatinine iminohydrolase, which catalyzes the production of ammonia from creatinine, can be immobilized on the surface of an ammonium ion selective electrode. There is no interference from creatine but some from the ammonium ions in blood and urine. 

Another biosensor is based on an ion-sensitive field-effect transmitter. Creatinine iminohydrolase is immobilized on the gate by cross-linking with bovine serum albumin in glutaraldehyde vapor. Creatinine iminohydrolase catalyzes the formation of N-methyl-hydantoin (and ammonia) from creatinine. The differential signal between a reference and sensing chip is proportional to creatinine concentration. 

Creatinine iminohydrolase / /-Methylhydantoin amidohydrolase Pyruvate kinase Lactate dehydrogenase NAD +... 

Creatinine iminohydrolase Creatinine iminohydrolase /V-Methylhydantoin amidohydrolase W-Carbamoylsarcosine amidohydrolase Sarcosine oxidase Red product of peroxidase on 4-aminoantipyrine and phenol Ammonia... 

The first system, devised in the University of Porto, Portugal, was a sensor array for the measurement of creatinine in urine [18]. It consisted of a creatinine iminohydrolase enzyme immobilized by entrapment using a chitosan membrane onto a nonactin ISE. Catalytic hydrolysis by the enzyme generated ammonium ion which was then directly detected. The system was completed with ISEs for ammonium, potassium, sodium and calcium which allowed to correct for any endogenous ammonium (by the first ISE) or for alkaline and alkaline-earth interference in the ammonium-based biosensor (the other three). Linear response ranges were between 0.1 and 10 mM, what permitted the resolution of the multicomponent determination by PLS method. Comparison with reference Jaffe method showed a satisfactory correlation, although the slope of obtained vs. reference values was rather low the obtained value was 0.87, whereas theoretical value should be 1.0. 

Magalhaes and Machado Creatinine iminohydrolase Potentiometric Creatinine/ 1 mM - - Urine [18]... 

Gutidrrez et al. Urease and creatinine iminohydrolase Potentiometiic Urea/1 mM Creatinme/l mM Ammonium/1 mM Potassium/1 mM Sodium /I mM Urine [20]... 

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