Proinsulin, a single-chain precursor of insulin, has been detected in biosynthetic studies in vitro,(1-4) and in crystalline preparations of insulin from several species.(1, 5-7) It appears that proinsulin normally serves neither as a major storage nor secretory form of the hormone.(8) Its primary functions seems to be to facilitate the efficient formation of the disulfide bonds of insulin.(9)Although several species of fish have two insulins differing slightly in primary structure,(10-12) the rat is the only mammal where this is known to be the case.(13, 14) As the two rat insulins are nonallelic(14) and presumably coded by two distinct genes, a separate proinsulin would be expected to precede each insulin. We have demonstrated the biosynthesis of both insulins(15) and of a proinsulin corresponding to each in isolated islets of Langerhans, and have detected probable intermediates in the conversion of these proinsulins to insulin. Labeled peptide material corresponding to the free connecting segment of proinsulin (C-peptide) was detected in insulin-containing fractions isolated from incubated rat islets. It was noted that islets incubated in vitro secreted small amounts of newly synthesized proinsulin as well as the two insulins and essentially equivalent amounts of C-peptide. Increasing the glucose content of the medium selectively enhanced the incorporation of radioactivity into proinsulin and insulin and also seemed to increase the relative proportion of labeled proinsulin appearing in the medium.

Animals↗

PubMed1968

The spontaneous reoxidation of reduced beef and rat proinsulins.

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Allergy and Immunology↗

PubMedDate not supplied

Influence of a continuous cimetidine infusion on lidocaine plasma concentrations in patients.

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Adult↗

PubMedDate not supplied

Comparison of two methods for determination of total solids content of milk: collaborative study.

Ten laboratories analyzed 9 pairs of blind duplicate raw milk samples for total solids. A direct forced air oven method (4 h at 100 degrees C) and a modification of the AOAC predry method (16.032) were used. Preliminary evaluation of the modified AOAC method indicated that blank determinations were necessary. Total solids content ranged from 12.0 to 14.6%. Average repeatability standard deviations (Sr) of the direct forced air oven and modified AOAC methods were 0.019 and 0.017, respectively. Average reproducibility standard deviations (SR) of the direct forced air oven and the modified AOAC methods were 0.042 and 0.047, respectively. Average repeatability relative standard deviations (RSDr) for the direct forced air oven and the modified AOAC methods were 0.149 and 0.136%, respectively; average reproducibility relative standard deviations (RSDR) were 0.327 and 0.370%, respectively. Mean repeatability values (r) and reproducibility values (R) were 0.054 and 0.118 for the direct forced air oven method and 0.049 and 0.133 for the modified AOAC method, respectively. The mean test result of the direct forced air oven method (12.7293%) was comparable to that for the modified AOAC method (12.7273%). The modification of AOAC method 16.032 and the direct forced air oven method have been approved interim official first action.

Animals↗

PubMedDate not supplied

Combination of total solids determined by oven drying and fat determined by Mojonnier extraction for measurement of solids-not-fat content of raw milk: collaborative study.

Each of 9 laboratories analyzed 9 pairs of blind duplicate raw milk samples for fat, using the Mojonnier ether extraction method (16.E13-16.E17), and for total solids, using a new direct forced air oven method. Solids-not-fat was determined by subtracting percent fat from percent total solids. The solids-not-fat content of the samples tested in the collaborative study ranged from 8.48 to 9.36%. The average repeatability standard deviation (sr) and the average reproducibility standard deviation (SR) for the solids-not-fat method were 0.019 and 0.041, respectively. Average repeatability (RSDr) and reproducibility (RSDR) relative standard deviations were 0.218 and 0.466%, respectively. The mean repeatability value (r) was 0.055; the mean reproducibility value (R) was 0.117. The difference between milk total solids determined by direct forced air oven drying and milk fat determined by Mojonnier ether extraction has been approved for interim official first action for determination of solids-not-fat content of milk.

Animals↗

PubMedDate not supplied

Comparison of Babcock and ether extraction methods for determination of fat content of milk: collaborative study.

Eleven collaborating laboratories analyzed 18 blind duplicate pairs of raw milk samples for fat by the Babcock method and by a modified Mojonnier ether extraction method in 7 round robins conducted over a 14 month period. Ten laboratories used the Babcock method and 10 used the modified Mojonnier method. Fat content of samples ranged from approximately 2.7 to 5.6%. Mean test value of samples analyzed was approximately 3.9% fat. Average standard deviations of within-laboratory repeatability (Sr) of the Babcock and ether extraction methods were 0.029 and 0.015% fat, respectively. Average standard deviations of between-laboratory reproducibility (SR) of the Babcock and ether extraction methods were 0.039 and 0.020% fat, respectively. Average repeatability relative standard deviations (RSDr) for the Babcock and ether extraction methods were 0.742 and 0.396%; average reproducibility relative standard deviations (RSDR) were 1.014 and 0.512%, respectively. Mean repeatability values (r) and reproducibility values (R) were 0.081 and 0.111% for Babcock and 0.044 and 0.056% for ether extraction, respectively. The ether extraction method demonstrated consistently better within- and between-laboratory agreement. The overall mean test value for the Babcock method was significantly higher (0.021% fat) than that for ether extraction. The difference between Babcock and ether extraction fat test results was different for different farms. In addition, the mean difference between percent fat determined by the Babcock and ether extraction methods was different in different months. There was no correlation in the difference between Babcock and ether extraction methods with the absolute level of fat in the samples in the range of 2.7 to 5.6% fat. The modifications of the AOAC Babcock method and the modified Mojonnier ether extraction method have been approved interim official first action.

Animals↗