**2. Introduction: molecular aspects of homocysteine**

Homocysteine is a sulphur-containing amino acid which is derived from methionine [6]. Methionine is activated by ATP to S-adenosylmethionine (SAM) [6]. In turn, S-adenosylhomocysteine (SAH) is produced from SAM by transmethylation process [6]. Subsequently, SAH is then hydrolysed into homocysteine [6].

Cystathionine β-synthase (CBS) has the role of catalysing the condensation of homocysteine together with serine into cystathionine by process of transsulfuration [6]. The conversion of cystathionine into cysteine depends on pyridoxal 5′-phosphate [6].
