Hydrolytic Proteins of Sugarcane: Amylase

Abstract

Amylase was extracted from lyophilized tissues of the meristem, leaf, sheath, node, and internode areas of 10-month-old sugarcane. Immature leaves (—1 and 0) were the richest source, while strong activity was also obtained with 8- to 10-node preparations. About 70 percent of the amylase of water extracts was precipitated with ammonium sulfate between 48- and 60-percent saturation. Both potato starch and amylopectin were readily hydrolyzed, although amylose, corn starch, and inulin were also acted upon. Maximum velocity was obtained with 8 mg. of amylopectin per milliliter of digest. Optimum pH was 5.5. Amylase was highly active between pH 4.5 and 6.0, and declined rapidly above pH 6. Amylase was almost inactive at 16° C , but increased seventeenfold to a maximum at 50° C. Both mercury and iodide completely inhibited amylase at 1 X 10^-4 µmoles/ml. of digest. The effects of iodide, and to a lesser extent of mercury, were reversed by increasing substrate concentrations. Magnesium partly inhibited the enzyme at 0.1 µmole/ml. Manganese stimulated amylase over the range of 0.003 to 0.60 µmole/ml. of digest. Thirty-six- to forty-eight-hour dialysis of amylase preparation against distilled water caused moderate activity decreases of 35 to 50 percent. The activity was readily restored with added manganese and traces of sugars. Sucrose was least effective, but maltose, galactose, glucose, and fructose all stimulated amylase activity above that of control, i.e. undialyzed, preparations. Several similarities were observed between amylase and invertase, including identical saturation ranges during salt fractionation, identical pH optima, similar responses to increasing temperature, inhibition by mercury, and activation by manganese and sugars. It is suggested that the amylases and α-glucosidase of sugarcane are very closely related, if not identical, and that a common property of the two types of enzymes is an affinity for α-glucosidic bonds.