Effects of tetrazolium salts on oxidative phosphorylation in rat-liver mitochondria

1. The effects of five different tetrazolium salts on oxidative phosphorylation in rat-liver mitochondria have been investigated. 2. In all cases the mitochondria were uncoupled by very low concentrations of the tetrazolium salts. Further, the transition from a system just exhibiting respiratory control to one in which the mitochondria were totally uncoupled has been shown to occur over very small concentration ranges of the tetrazolium salts. 3. The effectiveness of the five tetrazolium salts as uncoupling agents is discussed in the light of their standard electrode potentials and effectiveness as electron acceptors in dehydrogenase-linked reactions.     

Pyrimidine nucleotide synthesis in the rat kidney in early diabetes.

Early renal hypertrophy of diabetes is associated with increases in the tissue content of RNA, DNA, and sugar nucleotides involved in the formation of carbohydrate-containing macromolecules. We have previously reported an increase in the activity of enzymes of the de novo and salvage pathways of purine synthesis in early diabetes; the present communication explores the changes in the pathways of pyrimidine synthesis. Measurements have been made of key enzymes of the de novo and salvage pathways at 3, 5, and 14 days after induction of diabetes with streptozotocin (STZ), phosphoribosyl pyrophosphate (PPRibP), and some purine and pyrimidine bases. Carbamoyl-phosphate synthetase II, the rate-limiting enzyme of the de novo route, did not increase in the first 5 days after STZ treatment, the period of most rapid renal growth; a significant rise was seen at 14 days (+38%). Dihydroorotate dehydrogenase, a mitochondrial enzyme, showed the most marked rise (+147%) at 14 days. The conversion of orotate to UMP, catalyzed by the enzymes of complex II, was increased at 3 days (+42%), a rise sustained to 14 days. The salvage route enzyme, uracil phosphoribosyltransferase (UPRTase), showed a pattern of change similar to complex II. The effect of the decreased concentration of PPRibP on the activities of CPSII, for which it is an allosteric activator, and on activities of OPRTase and UPRTase, for which it is an essential substrate, is discussed with respect to the relative Ka and Km values for PPRibP and the possibility of metabolite channeling.     

Synapsis of a chromosomal pair heterozygous for a pericentric inversion and the presence of a heterochromatic short arm

Analysis of meiotic pairing configurations in a deer mouse heterozygous for both a pericentric inversion and the presence of a heterochromatic short arm at chromosome 15 revealed straight-paired synaptonemal complexes with equal axial lengths in a majority of the pachytene nuclei. Nonhomologous pairing in this bivalent occurs by direct heterosynapsis of the inverted segments followed by synaptic adjustment of the heterochromatin heteromorphism.     

Changes in pathways of pentose phosphate formation in relation to phosphoribosyl pyrophosphate synthesis in the developing rat kidney. Effects of glucose concentration and electron acceptors

Phosphoribosyl pyrophosphate (PPRibP), required in nucleotide synthesis, increases 2-fold in rat kidney from 1 day post partum to adult stage; there is no accompanying increase in PPRibP synthetase activity measured in vitro. Ribose 5-phosphate is a key factor in the regulation of PPRibP synthesis. The activity and regulation of 3 routes of ribose 5-phosphate formation have been measured in renal growth: (i) the flux through the oxidative pentose phosphate pathway was high in the neonatal period but increased only +50% thereafter; (ii) the non-oxidative pentose phosphate pathway, including transketolase, increased by +145%; (iii) the rate-limiting enzymes of the glucuronate-xylulose route increased +200% from 1 day to the adult stage. The importance of systems reoxidizing NADPH was shown by: (i) the stimulation of renal PPRibP formation from glucose by phenazine methosulphate; (ii) the early involvement of the oxidative pentose phosphate pathway at the stage where NADPH is used for biosynthetic routes; (iii) the increasing involvement of the glucuronate-xylulose route, which acts as a transhydrogenase producing NADP+ in addition to pentose phosphate formation and (iv) the correlation between renal PPRibP content and the activity of aldose reductase, which, by utilization of NADPH, stimulates ribose 5-phosphate formation via the oxidative pentose phosphate pathway. Evidence is adduced that the contribution of the 3 routes of ribose 5-phosphate formation in the kidney varies at different stages of development.     

Kininogen substrates for trypsin and cathepsin D in human,rabbit and rat plasmas

Studies have compared “total”, HMW kininogen and leukokininogen levels in human, rabbit and rat plasmas using trypsin, glass powder and cathepsin D as kininogenases or activators of kininogenases. Rat plasma was found to have about 10 fold more leukokininogen than the other plasmas assayed. When trypsin was used to estimate total kininogen, rat plasma liberated maximal amounts of kinin only in the presence of high concentrations of trypsin (1 mg/ml incubation mixture). In addition, it was found that trypsin in these concentrations liberated from rat plasma both bradykinin and a previously unidentified kinin which we have termed “T-kinin”. The results overall indicate that in the case of rat and rabbit plasma, currently used methods for estimations of total kininogen may not be accurate. T-kinin may represent a leukokininogen or a hitherto undescribed kininogen.