Although the reproducibility of motor unit number estimation (MUNE) for groups of subjects has been studied, there is little such data for individuals. Prediction intervals represent a tool to study individual MUNE reproducibility and represent the range of values expected for a future MUNE if the true number of motor units remains unchanged. MUNE was performed using the statistical method on 48 normal individuals. The prediction interval was found to be a function of the intrasubject coefficient of variation. Using a commercial manufacturer's recommended technique and software, prediction intervals were found to be so broad as to be of uncertain value. We found that by averaging two MUNE observations for each determination, and using the method of weighted averages for calculating the size of an average single motor unit potential, the intrasubject coefficient of variation was reduced from 16.48% to 8.77%, and the 90% prediction interval became sufficiently narrow to be clinically useful. False-negative rates were also lowered substantially using these techniques. Thus, simple modifications of an existing MUNE program improved the clinical utility of this program for the longitudinal study of patients in whom changes in motor unit number over time are of importance, such as those with motor neuron diseases.
The role of hexokinase in carbohydrate degradation in isolated, intact chloroplasts was evaluated. This was accomplished by monitoring the evolution of l4COZ from darkened spinach (Spinacia oleracea), maize (Zea mays) mesophyll, and Chlamydomonas reinhardtii chloroplasts externally supplied with "C-labeled frudose, glucose, mannose, galadose, maltose, and ribose. Clucose and ribose were the preferred substrates with the Chlamydomonas and maize chloroplasts, respectively. The rate of COz release from fructose was about twice that from glucose in the spinach chloroplast. Externally supplied ATP stimulated the rate of COz release.The pH optimum for COz release was 7.5 with ribose and fructose and 8.5 with glucose as substrates. Probing the outer membrane polypeptides of the intact spinach chloroplast with two proteases, trypsin and thermolysin, decreased ' T O p release from glucose about 50% but had little effect when fructose was the substrate.Tryptic digestion decreased COz release from glucose in the Cblamydomonas chloroplast about 70%. "COZ evolution from [1-14C]-glucose-6-phosphate in both chloroplasts was unaffeded by treatment with trypsin. Enzymic analysis of the supernatant (stroma) of the lysed spinach chloroplast indicated a hexokinase adive primarily with fructose but with some affinity for glucose. The pellet (membrana1 fradion) contained a hexokinase utilizing both glucose and fructose but with considerably less total activity than the stromal enzyme. Treatment with trypsin and thermolysin eliminated more than 50% of the glucokinase activity but had little effect on frudokinase activity in the spinach chloroplast. Tryptic digestion of the Chlamydomonas chloroplast resulted in a loss of about 90% of glucokinase activity. Saltman (1953), the first to investigate hexokinase in higher plants, observed that at least 20% of the total hexokinase activity in leaves was in the particulate cell fraction, the rest being in the cytosol. Resolution of the total hexokinase activity revealed four kinases in spinach leaves: two hexokinases active with Glc, Fru, and Man and two fructokinases functioning primarily with Fru but to a far lesser extent with Glc and Man (Baldus et al., 1981;Schnarrenberger, 1990). Essentially similar results have been described for pea seed (Copeland et al., 1978; Tumer and Copeland,
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