**Abstract**

The enzymes involved in the oxidative metabolism of n-6 polyunsaturated fatty acids, such as lipoxygenase (LOX) and cyclooxygenase (COX), are significant in the pathogenesis of colorectal cancer. The aim of this study is to estimate the effectiveness and partial purification of LOX and measure gamma-glutamyl transferase (GGT) activity in the serum of patients with colon cancer in Baghdad. The study included samples from 80 male patients with colon cancer and 50 samples of apparently healthy males (control) as the comparison group. The result displayed a noteworthy increase in lipoxygenase effectiveness (805.0 517.23 IU/L) in the serum of patients with colon cancer (stage pT3) compared with control (114.6 49.77 IU/L). The enzyme was purified by the precipitation of the serum protein using 40% (NH4)2SO4 and then removing the remaining salts by dialysis. The column of gel (Sephadex G.100) was used to separate the enzyme from another protein, in this step a single peak was obtained. The effective part of lipoxygenase is at yield 71.42% and folds 11.033. The ion exchange chromatography (DEAE–CeA50) was used to isolate LOX isoenzyme, and two bands (LOX1 and LOX2) were acquired with different degree of purity 16.372 and 12.16 folds, respectively. The result displayed a noteworthy increase in the GGT activity in patients (58.69 16.94 IU/L) compared with control (12.79 5.68 IU/L) p ≤ 0.0001. The increase in the activity of LOX can be potentially used as a tumor marker for colorectal cancer.

**Keywords:** colon cancer, lipoxygenase (LOX), gamma-glutamyl transferase (GGT), LOX isoenzyme, linoleic acid

### **1. Introduction**

Tumors usually arise as a result of mutations in the cellular DNA [1–7]. The mutations occur in two types of genes, oncogenes and tumor suppressor genes. Oncogenes stimulate cell division, and increasing the activity of these genes encourages cancer cells to grow abnormally and work on Protect cells from apoptosis. Tumor suppressor genes or apoptosis genes work to stop cell division and help the immune system protect tissue [8]. In the case of a tumor, these genes stop, because they oppose its formation by correcting errors in DNA transcription.

It should be noted that cancer occurs in all cases due to mutation, but not all mutations cause cancer. Cancer results from the abnormal activation of cellular genes that regulate cell growth and divisions. Determining the stage of the tumor expresses the extent of the tumor's progress and exacerbation and is necessary before starting the treatment. Thus we conclude that cancer is a disorder that results from the failure of cells to die, rather than the process of cell proliferation, as the proliferation is not matched by a sufficient number of cells that die, which leads to their accumulation [9–12].

The metabolism of fats in the human body, especially the arachidonic acid metabolism pathway, plays a major role in chronic inflammation and colon carcinogenesis [13], as phospholipase A2 (PLA2) enzymes stimulate the formation of free fatty acids such as arachidonic acid from phospholipids associated with the cell membrane, which have been shown to participate in the formation of cancer in laboratory mouse models [14].

LOX has an important role to stimulate inflammatory reactions. Reactive oxygen free radicals can cause inflammation that activates the release of cytokines and the activation of LOX. Inflammation is associated with many diseases, such as cancer, cardiovascular and neurodegenerative diseases. LOX contributes to the synthesis of leukotrienes and prostaglandins. These are associated with disease development [15]. The most important enzymes in the pathway of arachidonic acid metabolism [16] are LOX and COX, which are found in high concentrations in many tumors, including lung cancer [17], prostate cancer [18], brain cancer [19], rectal cancer [20], skin cancer [21], and breast cancer [22] where the GGT enzyme enters in the metabolic pathway of leukotrienes C4 [23].
