F.J.R. Hird

The importance of arginine in evolution

The special chemistry and metabolism of arginine has been considered in relation to the evolution of metabolic and structural features of animals. Arginine and compounds derived from it act in muscle as a major reserve of ATP and as a regulatory sink for phosphate. The metabolism of arginine in less complex animals has been extended to produce urea, firstly as an osmotic regulator and subsequently as a means for terrestrial animals to excrete surplus nitrogen. The ornithine component of arginine is metabolised to form important polyamines and also proline. It is also argued that the change from phosphoarginine to phosphocreatine was a permissive step in the development of the vertebrates which are rich in connective tissue.

Fatty acid binding proteins in the serum of various animals

Abstract 1. 1. A technique is described to study the binding of fatty acids to albumin in serum by use of thin-layer gel filtration. 2. 2. The presence of a protein which binds [14C]oleate is established in higher vertebrates, teleosts and a petromyzone. 3. 3. No fatty acid binding protein was observed in the six elasmobranchs studied and the results with crustaceans were ambiguous. 4. 4. The aspects of functional evolution of serum albumin are discussed.

Gluconeogenesis in vertebrate livers.

1. The hypothesis is advanced that it would be logical for a tissue (liver) to evolve as a gluconeogenic organ in order to recover the lactate produced as a result of rapid and sustained contraction of skeletal muscle. 2. Lactate was present in skeletal muscle of all animals examined and increased following electrical stimulation. It was also present in the blood. 3. Gluconeogenesis from lactate occurred in liver slices of all animals excepting amphibia. However, livers of these animals also contained much glycogen and are probably gluconeogenic. 4. Phosphoenolpyruvate carboxykinase was present in all animals investigated; pyruvate carboxylase was present in all animals excepting the toad.

A survey of the non-esterified fatty acids and binding proteins in the plasmas of selected animals

Abstract 1. 1. The levels of non-esterified fatty acids (NEFA) in the plasma of a variety of animals have been estimated. 2. 2. Only one of seven elasmobranchs contained detectable levels of NEFA. 3. 3. The two crustaceans examined contained very low levels. 4. 4. All the other animals contained circulating levels of a variety of NEFA ranging from 14 to 24 carbon atoms. 5. 5. The elasmobranchs are unique in that they also do not possess proteins in the serum which bind fatty acids.

Ketogenesis in vertebrate livers.

1. The hypothesis is advanced that a gluconeogenic organ such as the liver would evolve to oxidise fatty acids as its source of ATP for gluconeogenesis. It is also argued that such an organ might, in the light of current knowledge, be expected to be ketogenic. The animals investigated were lamprey, rainbow trout, eel, toad, axolotl, lizard and rat. 2. The respiratory quotients of liver slices from all animals was close to 0.74. Ketone bodies were produced from butyrate by all livers excepting the lamprey and ketone bodies were present in all blood samples examined. 3. There was no convincing evidence that direct deacylation of acetoacetyl CoA was important in any liver. HMGCoA synthase activity could not be found in the livers of the lamprey and eel. This enzyme was present in livers of the other animals. There was a large amount of acetoacetyl CoA-succinate transferase in the livers of the rainbow trout and eel, but only small amounts in the higher animals. 4. It is suggested that, initially the transferase was the important ketogenic pathway and the HMGCoA pathway evolved later.

Investigations on the origin and metabolism of the carbon skeleton of ornithine, arginine and proline in selected animals

The origin and metabolism of the carbon skeletons of the amino acids ornithine and arginine have been investigated in selected animals--an earthworm, an edible mollusc, a starfish, a sea-squirt, a freshwater crustacean and a rat. Only in the rat and microorganisms of sea water was any evidence obtained for the conversion of glutamate (or N-acetylglutamate) to ornithine. Apart from the crustacean, the other animals were able to synthesise the amidine moiety of arginine. All animals were able to hydrolyse (arginase) the amidine moiety from arginine and had the enzymic capacity to convert ornithine to proline. All the animals had some enzymic ability to oxidise proline to pyrroline-5-carboxylic acid. The crustacean (Cherax destructor) was able to conserve the high concentrations of arginine in its tail muscles during fasting. The hypothesis is put forward that, as arginine appears to be an essential amino acid in the diet of this animal, its demonstrated cannibalism is, among other things, a way of supplementing dietary arginine. The results are discussed in relation to the evolution of different phosphagens derived from arginine.

Oxidation of leucine by rat liver and kidney.

Abstract The oxidation of l -leucine-1-14C and l -leucine-U-14C to 14CO2 in liver and kidney tissue of the rat has been investigated. Kidney tissue was found to be the more active. Slices, homogenates, and mitochondria were able to oxidize this amino acid. Kidney slices converted all six carbon atoms to CO2 with approximately equal facility, but homogenates and mitochondria showed some loss of ability to oxidize C2-C6 to CO2. The results obtained using isolated mitochondrial systems are consistent with an initial deamination by transamination with α-ketoglutarate, an oxidative decarboxylation of the keto acid formed, followed by oxidation of the carbon skeleton by a process coupled with oxidative phosphorylation.

Oxidative deamination of glutamate and transdeamination through glutamate

Abstract Rat liver mitochondria are able to produce ammonia from glutamate at a steady rate under the conditions described. A system generating ADP from ATP is necessary for the continual deamination of glutamate. Maximum stimulation is reached with a hexokinase-glucose system in the presence of 0.2 m m ATP. The phosphorlyation control ratio (ammonia produced in the presence of hexokinase and glucose divided by ammonia produced in their absence) is of the order of four. Mitochondria incubated with glutamate at 38 ° for 30 minutes in the medium plus 0.5 m m ATP, retain the ability to increase their rate of glutamate deamination on the subsequent addition of hexokinase and glucose; they lose this ability if incubated for 20 or 40 minutes at 38 ° as a sucrose suspension. 2,4-Dinitrophenol increases the rate of ammonia production from glutamate and thus abolishes a rate-limiting step. Ammonia is produced from glutamate at both 25 ° and 38 ° but at a faster rate at the higher temperature. The phosphorylation control ratio in terms of ammonia is greater at 38 ° than at 25 °. Transdeamination of alanine and aspartate by rat liver mitochondria may be mediated by the addition of α-ketoglutarate or glutamate. Excess α-ketoglutarate (greater than 0.5 m m ) inhibits the production of ammonia from alanine and aspartate.

A re-appraisal of the function and synthesis of phosphoarginine and phosphocreatine in muscle

Abstract 1. 1. Three enzymic systems for the quantitative removal of inorganic phosphate from the medium have been investigated. They are: phosphorylase, glyceraldehyde-phosphate dehydrogenase and mitochondrial oxidative phosphorylation. 2. 2. Three enzymic systems and their substrates have been found to be functional for the synthesis of phosphoarginine and phosphocreatine from ATP. They are: phosphoglycerate kinase, pyruvate kinase and oxidative phosphorylation in association with arginine kinase and creatine kinase respectively. In the case of mitochondria from skeletal muscle, no exogenous creatine kinase was required. 3. 3. The hypothesis is advanced that arginine in invertebrates and creatine in vertebrates, by accepting phosphate, permit resting muscle after exercise to remove inorganic phosphate to rate-limiting levels in order to control glycogenolysis and glycolysis. The contraction-relaxation cycle causes the phosphate stored as phosphoarginine or phosphocreatine to flow back to reform a metabolic pool of inorganic phosphate. This role is regarded as additional to their usually accepted role as phosphagens.

The formation of ammonia from glutamine and glutamate by mitochondria from rat liver and kidney

Abstract The metabolism of glutamate and glutamine by mitochondria from rat liver and kidney has been investigated. Kidney mitochondria have been shown to be considerably more active both in rates of oxidation and in ammonia formation. The rapid oxidative formation of ammonia from both glutamine nitrogen atoms by kidney mitochondria could not adequately be explained in terms of glutaminase I (hydrolysis) or gutaminase II (transamination followed by hydrolysis) activity. The evidence obtained suggested additional pathway(s) but there is the possibility that permeability factors could be involved.