Heavy‐chain isoforms of non‐muscle myosin in human tissues

The heavy‐chain isoforms of myosin in human non‐muscle and smooth muscle tissues were analyzed by means of SDS/PAGE and using three distinct newly developed monoclonal anti‐(human cerebrum myosin) Ig (HBM‐1, HBM‐3 and HBM‐4). Purified cerebrum myosin contained three electrophoretic variants of non‐muscle myosin heavy chain (NM1, NM2 and NM3, with apparent molecular masses of about 200, 198 and 196 kDa, respectively). Both NM1 and NM2 were recognizable by the brain‐specific antibody HBM‐1, while NM3 was recognizable by HBM‐3. Each of the variants reacted with HBM‐4 to a similar extent. Purified cerebellum myosin gave three electropho retic variants of the heavy chain which were indistinguishable electrophoretically or immunologically from those of cerebrum myosin. Aortic myosin contained four electrophoretic variants, including the two smooth muscle myosin heavy chain isoforms and NM2‐like and NM3‐like heavy chains. Liver, platelet and kidney myosins contained a heavy chain very similar to NM3. Kidney myosin also contained a small fraction of an NM2‐like electrophoretic variant. In addition, cerebrum, kidney, liver and platelet myosins appeared to contain minor, 194‐kDa myosin heavy‐chain‐like polypeptide(s) (NM4). NM1, as well as NM2 and NM3, thus appear to be the brain‐type and non‐brain‐type non‐muscle myosin heavy‐chain isoforms, respectively, and additional minor heavy‐chain isoforms are also likely to be present in human tissues.