An enzymic microassay for starch

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Abstract
Conditions are described for measuring the starch content of plant tissues or extracts as glucose over the range from 10−7 mol to 10−14 mol. The method is based on the hydrolysis of gelatinized starch by amyloglucosidase; the glucose released is measured by reduction of NADP+ by coupled enzymic reactions.The NADPH is determined directly either spectrophotometrically or fluorimetrically, or after enzymic amplification. Amyloglucosidases were tested for contaminating enzymes which might degrade glucans other than starch, and a commercial preparation from Rhizopus niveus was found to be suitable for use without pretreatments. Glucose present in tissues and extracts may be measured and subtracted from starch values using appropriate blanks, or first destroyed by dilute alkali and heat. Addition of α‐amylase to amyloglucosidase during starch hydrolysis was not found to increase percentage hydrolysis from the normal range of 86–99% from starches of different sources.The procedures described are rapid and several orders of magnitude more sensitive than current methods, and can be used to measure the starch content of single cells.