Insulin degradation V. Unmasking of glutathione-insulin transhydrogenase in rat liver microsomal membrane

Characteristics of Thiol:Protein Disulfide Oxidoreductase from Wheat (Triticum aestivum L.) Grain

“…The temperature optimum for activity is around 33 38°C, with maximal activity at 36°C. NADP dependent wheat thioredoxin reductase has temperature optimum of 25°C [26], and the enzymes extracted from animal tissues had similar temperature optimum, 37°C [33,34].…”

How many distinct enzymes are responsible for the several cellular processes involving thiol:protein‐disulphide interchange?

“…Studies on insulin degradation using whole cells [7], homogenates [1][2][3]5,6] and sub-cellular fractions [4,8] show that the reduced A chain and various ill-characterised oligomers of the A and B chains are major products. Considerable evidence has been advanced showing that a two-step pathway of degradationreduction followed by proteolysis -occurs at both high and at physiological insulin concentrations [5][6][7].…”

“…Essentially two activities have been used for their analysis namely the reduction of insulin by GSH, to yield GSSG and reduced A and B chains [1][2][3][4][5][6][7][8] a type (1) reaction, and the thiol-dependent regain of enzyme activity from fully oxidised incorrectly disulphide-bonded ribonuclease ('scrambled' ribonuclease), a reaction of type (4) [64][65][66][67][68][69][70][71][72][73][74][75]. These two activities have been formally named glutathione: protein-disulphide (insulin) oxidoreductase (EC 1.8.4.2) and protein-disulphide isomerase (EC 5.3.4.1), respectively.…”

Phospholipid Composition of Liver Homogenates and Microsomes of the Lean and Obese Hyperglycemic (OB/OB) Mouse

“…The mice were almost 8 weeks of age at the time of sacrifice. The excised livers were homogenized using a Teflon-fitted Potter-Elvehjem homogenizer, and microsomes were prepared (13,14); these were kept frozen at -20" until used. The purity of the microsomal preparations was established by the assay of marker enzymes, which showed that they were free from mitochondria1 proteins as judged by almost complete absence of succinate-INT reductase ; the specific activity of glucose-6-phosphatase (a marker enzyme for the microsomes) was increased 4.5-fold over that of the homogenates.…”