World Applied Sciences Journal 17 (8): 941-946, 2012 ISSN 1818-4952 © IDOSI Publications, 2012 Corresponding Author: Jila Masrour Roudsari, Infectious Diseases and Tropical Medicine Research Center, Babol University of Medical Sciences, Babol, Iran. Tel: +98 111 2207924, Fax: +98 111 2207924. 941 Quantification of Liver Alkaline Phosphatase Isoenzyme Activity Using Heat Inactivation and Phenylalanine Inhibition Techniques: Comparison of Two Methods Soleiman Mahjoub and Jila Masrour Roudsari 1,2 3 Fatemeh Zahra Infertility and Reproductive Health Research Center, 1 Babol University of Medical Sciences, Babol, Iran Department of Biochemistry Biophysics, Faculty of Medicine, 2 Babol University of Medical Sciences, Babol, Iran Infectious Diseases and Tropical Medicine Research Center, 3 Babol University of Medical Sciences, Babol, Iran Abstract: Measuring serum alkaline phosphatase (ALP) isoenzymes activity is very important for evaluation of two groups of conditions including hepatobiliary and bone diseases. The present study aimed to compare phenylalanine inhibition and heat inactivation techniques in the quantification of liver ALP isoenzyme activity. Fasting serum from 50 healthy adults were used to evaluate total ALP and liver isoenzyme activities. Comparison of Intra- and inter-assay precisions for normal and cholestatic liver samples using phenylalanine inhibition (PI) and heat inactivation (HI) methods were done. Total alkaline phosphatase activity was 91.2 ±24.7 in 50 normal serum samples using IFCC standard method. Intra-assay coefficients of variations (CV) were 3.17% and 4.22% for normal and 2.98% and 3.75% for cholestatic liver samples using HI and PI methods, respectively. The inter-assay CV were 3.64% and 4.45% for normal and 3.23% and 4.06% for cholestatic liver samples using HI and PI methods, respectively. Moreover, correlation of HI and PI methods was found to be r = + 0.881 for liver isoenzyme. Regarding the appropriate precision and repeatability of the methods, as well as their cost effectiveness, they can be of use in the quantification liver ALP isoenzyme activity, especially in hepatobiliary diseases. Key words: Alkaline phosphatase Enzyme activity Liver isoenzyme Heat inactivation Phenylalanine inhibition Method INTRODUCTION oxalate and cyanide have all inhibitory effect on ALP Alkaline phosphatase (ALP) isoenzymes mainly exist phenylalanine, urea, excess Zn and arsenate ion lead to in bones, liver, intestine, placenta, mammary glands, selective inhibition of a number of isoenzymes [1-4]. kidneys and leukocytes. In normal serum, more than Measurement of serum alkaline phosphatase activity 90 percent of total alkaline phosphatase activity is related is of high significance for the evaluation of two groups of to bone and liver isoenzymes. Functionally, alkaline conditions including hepatobiliary and bone diseases phosphatase removes a phosphate group from associated with increased osteoblastic activity. In cases nucleotides and proteins. As the name suggests, the of simultaneous presence of bone and liver disorders, enzyme works optimally at basic pH levels. A number of measuring the activity of different isoenzymes has high bivalent ions such as Mg, Co and Mn have an activating clinical value, indicating the rate and the extent of the role and Zn is a structural component of the alkaline relative tissue damage. Laboratory analysis of blood phosphatase; whereas, ions such as phosphate, borate, specimens can detect abnormalities in ALP levels found isoenzymes. On the other hand, compounds such as L-