Comparative and evolutionary adaptation of muscle buffering capacity in species subject to varying degrees of acidosis.

Abstract

The Histidine (His) dipeptides, Carnosine (β-AlaHis) Anserine (β-Ala-1-methylHis) and Balenine (β-Ala-3-methylHis) are ubiquitous in muscle of vertebrates and invertebrates. Their major function appears to be H+ buffering in muscle, with the imidizole ring of the His residue having a pka of 6.7–7.1. Species variations in the quantity of His-dipeptides appears to be proportional to the level of anerobically generated H+ ions during naturally encountered bouts of exercise. Whale muscle, which contains the highest level of His-dipeptide of any species (>350 mmol.kg−1dm), is subjected to the greatest levels of anaerobic acidosis during prolonged oxygen deprivation. Pectoral muscle from birds such as wild pheasant (~220) have evolved high levels to combat H+ ions generated by explosive flight, a requirement for survival, but also a vestigial feature in the chicken (~225) and turkey (~275). Horses (~110), dogs (~82) and racing camels (~70) have selectively adapted higher muscle levels to counteract acute acidosis during sprints required for escape, hunting or racing. Humans, in contrast, have much lower levels; V lateralis in body builders (~44), omnivores (~23) and vegetarians (~13) are consistent with less need for sprinting for survival. CONCLUSION: Comparative levels of His-dipeptide in muscle from different species are reflective of the relative need for H+ buffering indicating evolutionary adaptation.