Glycerol can act as a substrate for glucose synthesis by conversion to dihydroxyacetone phosphate and an intermediate in gluconeogenesis. In order for citric acid cycle pyruvate, lactate, intermediates and the carbon skeletons of mainly amino acids to act as precursors for gluconeogenesis and these compounds must first be transformed to oxaloacetate. several of the carbon skeletons of the amino acids give increase to oxaloacetate straightly. Others feed into the citric acid cycle as intermediates and the cycle then converts these molecules to oxaloacetate. Lactate is changed to pyruvate through the lactate dehydrogenase reaction and some amino acids also provide enhance to pyruvate. Therefore, for these precursors the first step in the gluconeogenic pathway is the conversion of pyruvate to oxaloacetate.