What are the intermediary metabolism of carbohydrate? Write down about glycolysis in RBC.

Intermediary metabolism of glucose:

A. Anabolic

·        Glycogenesis

·        Gluconeogenesis

·        Lipogenesis

·        Uronic acid synthesis

B. Catabolic

·        Glycolysis ( Embden Meyerhof pathway)

·        Glycogenolysis

·        Hexos monophosphate shunt

·        Oxidation of pyruvate to acetyl CoA.

·        Tricarboxylic acid cycle (TCA cycle or Krebs cycle or Citric acid cycle)

There is two pathways in RBC for glycolysis.

1. Embden-Meyerhof pathway

2. Hexos monophosphate shunt.

·        Mature RBC have no mitochondria, so they are totally dependant upon glycolysis for ATP production.

·        Glycolysis in erythrocytes even under aerobic conditions always terminates in lactate because mitochondria that contain the enzymatic machinery for the aerobic oxidation of pyruvate are absent.

·        Enzyme involvement in glycolysis of RBC are hexokinase, glucokinase, pyruvate kinase.

·        End product of glycolysis is lactate and 4 ATP is produced in expenditure of 2 ATP. Net ATP production 2ATP.

·        Glucose is the only metabolic fuel for RBC and RBC derives energy from glucose by glycolysis. RBC uses this energy to feed Na⁺ - K⁺ pump necessary to maintain its biconcave shape.

BPG shunt (Rapaport – Leubering cycle):

·        This is a lateral extension of glycolysis that happens in RBC.

·        1-3BPG an intermediate of glycolysis is shunted away to make 2-3DPG which can again be converted to 3-PG to comeback to the main stream of glycolysis.

·        2,3BPG reduces the affinity of hemoglobin to oxygen and thus helps in oxygen unload from hemoglobin at tissue level.

Another glycolytic pathway in RBC is HMP shunt (Hexos-monophosphate shunt, Pentose phosphate pathway)

·        Here glucose 6-P is reduced to ribose sugar and NADP2H. No ATP is directly consumed or produced. The reaction is primarily catalyzed by glucose – 6 – phosphate dehydrogenase.

Role of HMP shunt in RBC:

Under the influence of different oxidants hemoglobin in RBC may turn into methemoglobin where ferrus iron of normal hemoglobin is converted to ferric form by losing one electron which is accepted by molecular oxygen to form superoxide. This superoxide causes lysis of RBC membrane and methemoglobin that is produced loses oxygen carrying capacity. Therefore to save RBC, superoxide must be metabolized to H₂O and to maintain normal hemoglobin function methemoglobin must be converted back to normal hemoglobin for these activities NADP2H provided by HMP shunt is needed.