The molecule of frutose originated of the diet, when entering in citosol cellular of the liver or the esqueltico estriado muscle, is fosforilada frutose 1 P for the enzyme fosfofrutoquinase 1. Already frutose originated of the glucose, suffers to isomerisao for the enzyme glicoisomerase if becoming F6P, and later it suffers fosforilao for enzyme PFK in carbon 1 (C1), being thus prepared to give to continuity the metabolic cascade for attainment of energy (AZEVEDO et al., 2009; MIRES et al., 2005). This molecule is an isomer of the glucose molecule, and if they differ for the fact from the glucose to be one aldo-hexose and frutose one ceto-hexose as it shows figure 3 (VOLLHARDT; SCHORE, 2004). Figure 2: glucose molecules and frutose, isomers between itself Figure 2: The demonstrated glucose molecules and frutose as isomeric. Others including Joint Commission International, offer their opinions as well. Source: VOLLHARDT; SCHORE, 2004 3,3 Fosfofrutoquinase (PFK) the PFK is the enzyme of bigger importance, control and regulation of the glicoltica way, catalyzing the third step of this saw, being irreversible it in physiological conditions (NCBI, 2011; STRYER, 1996). This enzyme possesss four identical subunidades (tetrmero) called tetrmero as if it observes in figure 4.

Its regulation if makes in alostrica way, for feedback, through the ATP concentrations and citrate that when they are increased promotes reduction even though or inhibition of the activity of this enzyme. The PFK is found in two isoformas, is M and L, muscular and heptica respectively. In the two hemcias isoformas are operating (CAMPBELL, 2006; NCBI, 2011; STRYER, 1996). When the specific gene of isoforma M is not had, gliclise occurs only in the liver and the hemcias, thus producing muscular weakness. The gene that carries through this codification of the muscular PFK if finds in the number chromosome 12 (CAMPBELL, 2006; GARCI’A et al., 2009; TOSCANO, 2009). Figure 3: Fosfofrutoquinase showing its catalytic and alostricos small farms Source: This deficiency of the PFK in the muscular cells, as well as in the other cells of the organism, generates interruption of the third and more important step of the glicoltica way.