Antisense inhibition of isoamylase alters the structure of amylopectin and the physicochemical properties of starch in rice endosperm

This is the first report on regulation of the isoamylase1 gene to modify the structure of amylopectin and properties of starch by using antisense technology in plants. The reduction of isoamylase1 protein by about 94% in rice endosperm changed amylopectin into a water-insoluble modified amylopectin and a water-soluble polyglucan (WSP). As compared with wild-type amylopectin, the modified amylopectin had more short chains with a degree of polymerization of 5-12, while their molecular sizes were similar. The WSP, which structurally resembled the phytoglycogen in isoamylase-deficient sugary-1 mutants, accounted for about 16% of the total alpha-polyglucans in antisense endosperm, and it was distributed throughout the whole endosperm unlike in sugary-1 mutant. The reduction of isoamylase activity markedly lowered the gelatinization temperature from 54 to 43 degrees C and the viscosity, and modified X-ray diffraction pattern and the granule morphology of the starch. The activity of pullulanase, the other type of starch debranching enzyme, in the antisense endosperm was similar to that in wild-type, whereas it is deficient in sugary-1 mutants. These results indicate that the isoamylase1 is essential for amylopectin biosynthesis in rice endosperm, and that alteration of the isoamylase activity is an effective means to modify the physicochemical properties and granular structure of starch.

Three methods compared for isoamylase separation in tissue homogenates

Using homogenates of autopsy tissue, we compared three widely available techniques for separating amylase isoenzymes: wheat-germ inhibition (WI), and electrophoresis on cellulose acetate (CA) or agarose (AG). WI separated amylase into two isoforms, CA into seven (three pancreatic and four salivary), and AG into nine (five pancreatic and four salivary). CA and WI had similar isoamylase detection limits (8-10 U/L) and similar imprecision in measuring percent S-type vs P-type isoamylase (within-run SD 1-2%), and they demonstrated a linear response to added S or P isoamylase. In contrast, the AG method had higher detection limits (10-15 U/L), greater imprecision (within-run SD 3%), and showed a nonlinear response to added S or P isomylase. We conclude that CA and WI have essentially equivalent assay attributes, superior to AG, but that CA resolves more amylase isoforms than WI.

Passage of salivary amylase through the stomach in humans

With an inhibitor assay technique rates of passage of salivary and pancreatic isoamylase through the jejunum were measured in six healthy volunteers after different liquid, intragastric meals. In all subjects and in 13/17 experiments, more than 2500 units of salivary amylase were passed over 200 postcibal minutes. Salivary amylase comprised 13.8 +/- 3.9% (mean +/- SEM) of the total amylase and appeared predominantly as single, distinct peak. The inhibitor method was validated by isoelectric focusing (r = 0.988; P less than 0.001; N = 7). The frequency of detection of salivary amylase in gastric or jejunal samples fell as gastric pH fell below 3.0. In vitro, amylase was inactivated in gastric juice as pH fell between 3.8 and 3.3. Salivary amylase accounted for 11% of total amylase output in a normal and 27% in an achlorhydric subject after a hamburger meal. We conclude that amylase should not be measured in postprandial studies of pancreatic secretion in humans without correction for salivary amylase.

Evaluation of a new inhibitor test for isoamylase on Hitachi 705 analyser

We describe a simple and rapid method for measuring pancreatic and salivary type amylases using the Hitachi 705 analyser. The determination is based on the inhibition of salivary amylase using an inhibitor isolated from wheat germ. The precision of the proposed method was very good: within-day precision varied from 0.4 to 2.5% (CV) and day-to-day precision from 2.2 to 3.7% (CV). The new application correlated well with another commercially available inhibition method. As the standardization is very stable and the assay procedure exactly the same as for the total amylase assay, the proposed method is suitable for routine isoamylase determination. Reference values for pancreatic and salivary amylase activities are presented.

Evaluation of a new procedure for isoamylase measurement by selective inhibition

The authors have evaluated a new procedure for the estimation of pancreatic and salivary isoamylase using a new selective inhibitor reagent (Enzamyl Isoamylase, Gödecke), Germany; composition covered by patent No. P 3404876.6). Provided the conditions of the assay presented here are correctly selected, a standard curve is not necessary and the activities of both isoenzymes can be calculated by a simple formula. In view of its rapidity and precision, this new procedure appears to be useful as a screening test. It correlates closely with a reference electrophoretic method.

Serum amylase and isoamylase assay on the Hitachi 705 automatic clinical chemical analyzer

The automated continuous alpha-amylase assay using p-nitrophenyl-alpha-D-maltoheptaoside (Boehringer Mannheim) as substrate on the Hitachi 705 clinical chemical analyzer, was compared with the Phadebas Kinetic Amylase Assay (Pharmacia Diagnostics) on the Hitachi 705. The two methods showed good correlation. The precision varied from 1.0 to 2.5% (CV) within-day and from 1.1 to 5.6% (CV) day-to-day. The substrate, p-nitrophenyl-alpha-D-maltoheptaoside, was also applied to an automated isoamylase assay. The amylase inhibitor from wheat was used to determine the ratio of pancreatic and salivary amylase activities of serum. About 80% of salivary type amylase was inhibited up to an activity level of 1000 U/l, while inhibition of pancreatic type amylase activity was only 10-15%. Ratios of pancreatic to salivary amylase from 0.1 to 10 can be evaluated in serum with wheat inhibitor. The precision of the isoamylase determination by the Boehringer amylase method was acceptable.

Evaluation of an inhibitor assay to determine serum isoamylase distribution

We tested a technique to distinguish salivary from pancreatic isoamylase using a wheat protein which inhibits salivary isoamylase. The inhibitor technique accurately reflected the preponderance of pancreatic or salivary isoamylase in sera which had been "spiked" with human pancreatic or salivary isoamylase. Comparison of the results of either cellulose acetate electrophoresis or isoelectric focusing showed an excellent correlation (r = 0.99) in 43 hyperamylasemic sera which did not contain macroamylase. Normal values obtained in 160 healthy subjects indicated that pancreatic isoamylase comprised 41 +/- 21% (1 SD) of total serum amylase activity and the upper limit of normal for serum pancreatic isoamylase was 166 IU/liter. The inhibitor assay provides a simple and accurate means of differentiating salivary from pancreatic hyperamylasemia.

[Serum isoamylases determination. Analytical and critical study of a new method using an inhibitor protein]

A new method for the serum isoamylase assay is studied. Its principle is the use of an inhibitor protein from wheat, mainly active on the salivary type isoamylases. Amylase remaining in the presence of the inhibitor (R) and total amylase (T) are measured and the R/T ratios calculated. The kinetic of the inhibition is studied with various samples of pancreatic juice and saliva, of which the isoenzymatic pattern has been evidenced by electrofocusing. The results show that 80% of the salivary type isoamylases (S) and 20% of those from pancreatic type (P) are inhibited in the operational conditions described. The inhibition is stopped, but not modified, by addition of amylase activity substrate. The analytic study of the kit showed convenient results. The chemical inhibition methodology is compared with a modified Davies' electrophoretic technic on cellulose acetate membrane. The results are shown on a diagram: R/T ratio on the ordinate and total amylasemia on the abscissa. In the middle of the diagram appears an area which corresponds to normal values obtained with 69 healthy subjects from 20 to 30 years old.