TRIPHOSPHOPYRIDINE NUCLEOTIDE‐DEPENDENT ENZYMES IN THE DEVELOPING SPINAL CORD OF THE RABBIT ^{1, 2}

Abstract

Abstract— Total lipid and the activity of five enzymes closely related to the generation of NADPH have been measured in the anterior horn region and dorsal columns of rabbit spinal cord during the period of rapid myelination. Lipid deposition progressed to a much greater extent in the dorsal columns than in the anterior horn region; however, the age at which one‐half of the total adult level of lipid accumulated in both regions was the same, i.e. 19‐20 days after birth. During the first 15 days of postnatal development of the dorsal columns, glucose‐6‐phosphate dehydrogenase changed in parallel with lipid content; however, in the anterior horn region changes in lipid were not accompanied by increases in glucose‐6‐phosphate dehydrogenase. In contrast to changes in glucose‐6‐phosphate dehydrogenase, the activity of malic enzyme increased in the anterior horn region but remained relatively constant in the dorsal columns during development. The activities of two other enzymes of the pentose phosphate pathway, 6‐phosphogluconate dehydrogenase and transketolase, measured at various intervals after birth, did not directly parallel changes in the activity of glucose‐6‐phosphate dehydrogenase in the dorsal columns. In both areas of the developing spinal cord the activity of NADP + ‐dependent isocitrate dehydrogenase was greater than the activities of the other three dehydrogenases but it did not parallel changes in lipid content of either region. A relationship between the requirements for reducing equivalents and the activities of the four NADP + ‐dependent dehydrogenases is suggested by the finding that both areas of the adult spinal cord contained lower activities of these enzymes than those observed during the initial 26 days of development. The differences noted in the two areas of the spinal cord during development suggest that mechanisms for the generation of NADPH differ in gray and white matter.