Investigation on the protein constituents of nerve Axoplasm

Abstract

Studies made in the past on the proteins of nervous tissue have been carried out almost exclusively with the large masses of material available in the brain and spinal cord of vertebrates. Because of the great complexity of such material it has been impossible to determine the position of the proteins in the various histological components of the neuron. It is uncertain, for example, which of the proteins are characteristic of the axis cylinder on the one hand and of such structures as chromatin or Nissl substance of the cell body on the other. Recently, Schmitt and Bear (1935), realizing this situation, began studies of the proteins of crustacean peripheral nerve. This tissue was chosen both because it consists predominantly of axoplasm and because its low lipoid content allows direct extraction of the proteins without preliminary desiccation or lipoid removal. It was found that the largest part (about 65%) of the protein of the entire nerve (including connective tissue) is extracted in neutral salt solutions and that the properties of this soluble protein are in many respects similar to those described by previous investigators working with mammalian central nervous system, the most reliable results being those of McGregor (1917). Though the amount of this fraction agrees roughly with estimates of the relative amount of axis cylinder in crustacean nerve (Young 1936), it was still not certain that all the components of the conjugated protein present could be considered to be derived solely from axoplasmic protein, for it was demonstrated that in lobster nerve an alkali-soluble fraction similar to the“neurostromin” of Danilevsky (1891) and Shkarin (1902) is also present. The axoplasm of the giant nerve fibres of Loligo may be obtained merely by extrusion from a cut end. In this way it is possible to obtain the axoplasmic complex uncontaminated by foreign material. The present paper contains a preliminary account of the properties of the proteins of the axon as revealed by study with a special microtechnique of this extruded axoplasm.