BIOLOGY OF SPERMATOZOA 



761 



Although this material can he oxidized hy 

 sperm with an R.Q. of about 0.71, there is no 

 detectable change in lij^d phosphorus (Har- 

 tree and Mann, 1959) ; rather, it is the fatty 

 acid residue which is oxidized. Whatever 

 the precise composition and nature of the 

 intracellular oxidizable reserves, the supply 

 nuist be fairly copious and the utilization 

 efficient; some 20 years ago Moore and 

 Mayer (1941) showed that ram sperm can 

 remain motile in neutralized seminal j^lasma 

 for 20 hours or more after the sugar, and 

 presumably other exogenous stores, are ex- 

 iiausted (see Lardy, Winchester and Phil- 

 lips, 1945). The details of lipid oxidation in 

 spermatozoa have not been elaborated, but 

 it is assumed that, as in other tissues, the 

 fatty acid residues react with acetyl-Co- 

 enzyme A and enter the tricarboxylic acid 

 cycle to be ultimately oxidized to carbon di- 

 oxide and water. 



Earlier work had established that the 

 addition of amino acids, particularly gly- 

 cine, to suspensions of fowl or bull sperm 

 increases many fold the duration of motility 

 and in fowl sperm stimulates oxygen con- 

 sumption as well (Lorenz and Tyler, 1951; 

 Tyler and Tanabe, 1952). No utilization of 

 the amino acids was detectable and the phe- 

 nomenon was interpreted on a basis of the 

 chelation of heavy metal ions, such as 

 occurs, for example, with ethylenediamine- 

 tetraacetate (Versene) (Tyler and Roths- 

 child, 1951). More recent experiments in- 

 volving the use of C^'*-labeled glycine have 

 shown that this amino acid is actually taken 

 up and metabolized by sperm of the bull, 

 without, however, increasing oxygen con- 

 sumption (Flipse, 1956; Flipse and Alm- 

 ([uist, 1956; Flipse and Benson, 1957). 

 (ilucose depressed but did not eliminate, 

 the utilization of glycine; on the other 

 hand, the addition of glycine had little or no 

 effect on the utilization of glucose (Flipse, 

 1958). The principal pathway of glycine 

 catabolism in sperm seems to involve gly- 

 oxylate, formate, and carbon dioxide. This 

 is similar to the scheme of glycine oxidation 

 in rat liver and kidney (Nakada and Wein- 

 house, 1953). Certain other amino acids, 

 namely phenylalanine, tryptophan, and ty- 

 i-osine, also are metabolized by sperm of 

 the bull and ram by a process of oxidative 



deamination catalyzed by the enzyme, l- 

 amino acid oxidase (Tosic, 1947, 1951). 

 Hydrogen peroxide is produced in this re- 

 action and is toxic unless eliminated by 

 catalase (Tosic and Walton, 1950). Thus it 

 is clear that certain amino acids are oxi- 

 dized by sperm, but the significance of these 

 reactions to the total energy-producing 

 metabolic processes of the cells cannot be 

 regarded as great. 



D. EPIDmVMAL SPERM AND METABOLIC 

 REGULATION 



Striking differences have been claimed for 

 the metabolic behavior, in vitro, of bull 

 sjx'rm, from different segments of the epi- 

 didymis, suggestive of metabolic regula- 

 tion in relation to sperm maturation in the 

 male genital tract (Henle and Zittle, 1942). 

 These differences are manifested by lower 

 rates of endogenous respiration and aerobic 

 glycolysis, and a higher rate of anaerobic 

 glycolysis, by epididymal sperm as com- 

 pared with the rates shown by washed sperm 

 of semen (Lardy, Hansen and Phillips, 

 1945; Lardy, 1952). Inasmuch as the motil- 

 ity of the spermatozoa from both sources 

 is essentially similar, such metabolic be- 

 havior indicates a higher biochemical effi- 

 ciency of the epididymal sperm. One can 

 indeed demonstrate an inhibition of gly- 

 colysis by oxygen (the Pasteur effect) in 

 epididymal sperm which is less readily dis- 

 played by washed seminal sperm. 



In a search for the cause of these differ- 

 ences. Lardy found evidence for a so-called 

 metabolic regulator which is present in a 

 bound or inactive form in epididymal sperm 

 and which is released or becomes active at 

 the time of ejaculation (Lardy, Ghosh and 

 Plaut, 1949). The action of the regulator 

 was thus considered to increase respiration 

 and aerobic glycolysis to levels character- 

 istic of semen. This regulating activity was 

 tentatively identified with a sulfur-contain- 

 ing component extractable from semen and 

 from testicular tissue; its action w^as found 

 to be similar to that of cysteine and reduced 

 glutathione (Lardy and Ghosh, 1952; Mann, 

 1954). Relatively little work has since been 

 done to identify further the metabolic reg- 

 ulator or to demonstrate a similar agent in 

 other species of sperm. 



