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61.
Cotton ovules cultured in an insufficiency of boron (10 micromolar), showed inhibition of fiber growth by the ninth day in culture. Averaging data from eight to eleven days of culture under these conditions, total incorporation of [6-14C]orotic acid into fiber was inhibited by 59%. Inhibition was evident in all radioactively labeled pools, indicating that the effect may be at the membrane transport level or at an early stage of orotic acid metabolism. On a per cent basis, incorporation into RNA under boron deficiency was higher than under sufficiency. The effect is greater on the eighth day of culture, with a decreasing difference from controls up to the eleventh day. Conversely, the per cent incorporation into UDP-glucose was lower under boron deficiency than in controls, having a more or less constant value from 8 to 11 days of culture. Thus, a primary event of boron deficiency in cotton fiber culture is an alteration in the flow of metabolites through the pyrimidine synthesis pathway. 相似文献
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Peripheral levels of progesterone and estradiol 17beta were quantified in 27 cycling cows following administration of a single Hydron ear implant (G. D. Searle and Co.) containing 2, 4 or 6 mg norgestomet or controls which received no implant. Implants were inserted subcutaneously in the ear on day 15 of the estrous cycle (day of estrus = day 0) and removed 9 days later. The 4 mg (seven of seven cows) and 6 mg (six of six cows) implants suppressed estrus; however, three of eight cows in the 2 mg group exhibited estrus prior to implant removal. The 6 mg implant group had a significantly longer interval from implant removal to estrus than either the 2 or 4 mg group. Failure to detect differences in the rate at which progesterone declined indicated norgestomet treatment did not affect normal corpus luteum regression. Estradiol levels rose at a similar rate approaching estrus in all treatments. There was no indication of increased endogenous estradiol levels due to norgestomet treatment. 相似文献
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NADP- and NAD-dependent glucose dehydrogenase was partially purified from a dark-grown blue-green alga (endophytic Nostoc strain MAC). Polyacrylamide gel electrophoresis established that a single protein possessed dual activity for either NADP or NAD. No other electron acceptor substituted for pyridine nucleotides and no evidence for a flavin prosthetic group was found. Although the Km for NADP was 8.8 mum and for NAD 328 mum, the enzyme was equally active with NAD or NADP at saturating levels of substrates. The enzyme was similar to previously described glucose dehydrogenase in that it had a high Km for glucose (18-20 mm at 35 C) and an alkaline pH optimum of 7.6 to 9.4. 相似文献
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A revision of the Schoenheimer-Sperry method for cholesterol determination 总被引:128,自引:0,他引:128